: For instance, technically, some teach "false doctrine" when they suggest that Abimalech was a judge. Factually speaking, he was a usurper king, not a judge. This "truth," though, doesn't really draw us any closer to God or affect our salvation.

While the "technicality" may be true (calling Abimelech a judge is in fact an error), the illustration tends to trivialize the concept of what false doctrine is, and how the phrase is used in the New Testament. Do you know that you can squirt lighter fluid on your hand, light it, and let it burn without pain or harm? Therefore, there's no harm in being on fire... Right? No. Such illustrations are not truly informative or helpful. Children still needed to be warned against playing with fire, and Christians need to be informed against false teaching.

On the one hand, understanding what the Bible says, even in Judges, is very helpful and important. Misunderstanding or misrepresenting the stories of scripture is detrimental, and yes, it can affect our salvation, because at the very least every untruth diminishes our understanding of truth and of God. Nevertheless, the diminutive illustration of Abimelech tends to trivialize the repeated warning against false doctrine, false teachers, and false prophets in the New Testament, rather than inform determination of what does matter. Of course people sometimes make major issues of minor misunderstandings, but there still remains an urgent series of warnings against following false teachers, false prophets, false teachings, and for that matter false brothers. It is seriously important to understand what the truth is, and teach it to others. You know the Old Testament illustrations. Whether to carry the ark of the covenant on shoulders or on an ox-cart was not trivial. Who put incense on a censor was a matter of life and death. It had nothing to do with morality or conscience, it had to do with the holiness of God, how people perceived him, and he was deadly serious about it.

: We all have a healthy aversion to divvying up the Bible into "essentials" and "non-essentials," and I want to stay as far away from doing that as possible. I think it is all essential, even Jesus' command (it's one of the clearest imperatives given) to wash one another's feet. The problem is that it is essential to the extent that our intellects understand it. It is not essential to the point of rejecting our brother who does or does not follow that command as we think he should.
: In other words, one brother thinks he is following that command by whipping out a foot basin when he meets with his church family, and another thinks he is following it by serving his brethren in any situation he can. I believe the latter, but I don't think it's necessary to divide from a brother who believes the former.

It's well and good, very Christian, to tolerate people of other opinions, and make every effort to live in peace with them. However, as you know there is a general tendency to insist that others accept "our" sensibilities, and that will always be a problem. I don't care if someone wants to offer a service of foot washing to a guest in their home (culturally odd, rarely useful in our times and circumstances, but perhaps a good work, 1 Tim 5:10). I care very much if someone tries to impose that as a sacrament of the assembled church or defines it as a necessary "act of worship."

The idea that something is "essential to the extent that our intellects understand it" is only partly true. While Paul would warn that "if anyone regards something as unclean, then for him it is unclean" (Rom 14:14), he would also assert that "my conscience is clear, but that doesn't make me innocent" (1 Corinthians 4:4). We can indeed bind things on ourselves, making them essential by our (flawed) understanding. However, many things are essential whether we understand them or not, physically and spiritually. Violating our conscience is almost always an error, but following our conscience may not be at all acceptable to God, and failing to do something God has commanded is wrong whether our intellects understand it or not.

: Your dilemma is good to point out the fact that there is a difference between "moral doctrine" and other types of doctrine. I believe our morality comes from God, not the written words of the Bible. This may seem controversial until you think about it for a second...murder and adultery aren't wrong because they are written in the Decalogue. The Decalogue doesn't rule us today. Murder and adultery are wrong because they go against God's nature. Hatred is wrong for the same reason, not because Paul listed it as a vice in one of his letters.

Frankly, I don't perceive the stated dichotomy between "'moral doctrine' and other types of doctrine." Do we pick and choose what is moral doctrine? Do confession, prayer, the Lord's supper, baptism, assembling with the church, etc. fall in or out of the category? How do we work through Ephesians 4-6 (for example) and sort the teachings into two columns, moral and spiritual (or whatever)?

Regarding "moral doctrine" you seem to refer to the "law of conscience" or things that men know by nature as referred to in Romans 2:14, but Paul doesn't teach that man without revelation is able to please God, or live righteously, or even has a consistent standard. Rather he teaches that all men, with and without God's revealed word (the Bible), fail to live righteous lives and are sinners by their own standards, by whatever they do believe. Saying that "our morality comes from God, not the written words of the Bible" strikes me as a little bit like saying, "the beef in my grocery store comes from Harris Ranch, not from cows." God's moral standards are part of his design for man, but they are revealed to us in his written word, and there is no other source for knowing with certainty just what our moral doctrine (and every doctrine) ought to be. Man starting from himself will not arrive at Biblical, which is to say God given, morality. "Indeed, I would not have known what sin was except through the law. For I would not have known what coveting really was if the law had not said, 'Do not covet.'" (Romans 7:7) Human moral systems always have some moral truth of course, but no one can or will derive a Godly moral system apart from God's revealed word.

: God gave us all a conscience pre-formatted with a moral code, and Romans 1:18-32 tells us how God views those who reject the moral code that He made to be self-evident.

Paul does assert that "God's invisible qualities, his eternal power and divine nature" can be discerned in the created realm. He does not assert quite as much as a "conscience pre-formatted with a moral code." God did design us to have a conscience, but it is surely not pre-formatted with a moral code. Moral codes are learned. Children have to be taught what is right and wrong, and so do converts to the Christian faith. Paul teaches in Romans 1:18ff that as men abandon God they in turn are given up by God to deeper and deeper moral turpitude, but he does not say that men begin by inherently knowing the difference between right and wrong. Paul emphasizes the failure and downward trend of human morality apart from God, climaxing the discussion in Romans 3:21-23 with the assertion that "all have sinned and fall short of the glory of God" but that now a "righteousness from God... has been made known, to which the Law and the Prophets testify." A conscience is built in, but it is far from morally adequate, and is not even stricly followed with all its learned flaws. Knowing what God does and wants is not innate or pre-formatted, it is revealed, and the Bible is the means of revelation

: Where I'm going with this is that moral issues seem to be off the table as far as contradicting opinions go. Some legalistically argue from scripture that cocaine is OK because God gave us all the herbs of the field to use, but we know that doesn't make it OK. It should be self-evident from our God-endowed conscience that it is immoral to get stoned, drunk, or otherwise recreationally intoxicated.

Moral standards are not negotiable, but lots of things are off the table, whether we see them intuitively or not, because God has spoken, and not only about moral issues. I don't see that Paul had any moral issue with the "false brothers" he denounced in Galatians 2:4 (unless we define moral issues much more broadly than the examples you've cited, incorporating everything that is right or wrong in God's sight), he took issue with their insistance that circumcision was required for Christians, because God had taught differently, through his apostles. Regarding moral behavior, it clearly is not self-evident to many people that acts and attitudes God disapproves are unacceptable. In terms of intoxicants, there are people who believe and teach that some forms of intoxication are not only morally acceptable but spiritually enlightening. Many believe that occassional intoxication is innocent fun "as long as they don't hurt anyone." They may be wrong, but neither their experience nor their conscience betrays the error in what they believe, what they do, and what they say. The world follows its own values, at odds with God's values, and suffers no particular pangs of conscience for doing so. It is not self-evident to millions of our fellow Americans that sex before marriage or cohabiting without marriage is wrong, and their consciences are not being ignored, they just don't have the standards as a matter of their training and conviction. There is no final way to insist on any moral (or spiritual) absolute if there is not a legitimate religious (Biblical) basis for it. Everything is ultimately negotiable apart from the specific revelation of God's word. That is true of moral and religious behavior. There is a standard, but it is not innate in the human heart, and it can be readily ignored without any particular awareness of being wrong.

: When people reject the conscience that God gave them in pursuit of their own lusts, it's not a mere "difference of opinion." We do have an obligation to reject immoral brethren from our Christian associations, which would imply that we would not baptize someone who was continuing unrepentantly in immoral behavior.

It isn't just about rejecting conscience, which is flawed. It's about rejecting God, and his revelation.

Jer 17:9-10
9 "The heart is deceitful above all things,
And desperately wicked;
Who can know it?
10 I, the LORD, search the heart,
I test the mind,
Even to give every man according to his ways,
According to the fruit of his doings.
NKJV

It is interesting, I think, and perhaps pertinent, to notice some of the times that God says people have rejected him. It's not usually about immoral behavior, rather that seems to follow from rejection instead of precipitating it.

In Numbers 11:20 Israel is said to have rejected the Lord because they are complaining about what God has (and hasn't) given them.

In Deuteronomy 31:20 it is prosperity and ease that lead to idolatry and rejecting God. (Likewise in 32:15)

In 1 Samuel 8:7 it is rejecting the tribal and priestly leadership and asking for a king (like everybody else) that is described as rejecting the Lord. (Likewise in 1 Samuel 10:19)

Somewhat different, but Saul in 1 Samuel 15:23 is not convicted of any moral failure, except that of "rejecting the word of the Lord" when he didn't do what God had commanded through Samuel. "Rebellion is like the sin of divination, and arrogance like the evil of idolatry."