One thing you'll quickly notice if you make even a casual study of historical theology is this: the history of the church is a long chronicle of doctrinal development that runs from one profound controversy to the next.
In one sense it is sad that the history of the church is so marred by doctrinal conflicts, but in another sense that is precisely what the apostles anticipated. Even while the New Testament was still being written, the church was contending with serious heresies and dangerous false teachers who seemed to spring up everywhere. This was so much a universal problem that Paul made it one of the qualifications of every elder that he be strong in doctrine and able to refute those who contradict (Titus 1:9). So the church has always been beset by heretics and false teachings, and church history is full of the evidence of this.
Obviously, then, we who love the truth cannot automatically shy away from every fight over doctrine. Especially in an era like ours when virtually every doctrine is deemed up for grabs, Christians need to be willing and prepared to contend earnestly for the faith.
On the other hand, even in an obsessively "tolerant" age such as ours, the opposite danger looms large as well. There are some people who are always spoiling for a fight over little matters, and no issue is too trivial for them to overlook. It seems they are looking for reasons to take offense, and if you're not careful what you say or how you say it, they'll throw a major hissy. More often than not, it's an insignificant issue, an unintentional slight, or an inadvertently indelicate "tone" that provokes the tantrum. (Ironically, these same folks are sometimes more than willing to tolerate major doctrinal errors in the name of "charity.")
Scripture includes all the following commands: "If it be possible, as much as lieth in you, live peaceably with all men" (Romans 12:18). "It was needful for me to write unto you, and exhort you that ye should earnestly contend for the faith which was once delivered unto the saints" (Jude 3). "If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed: For he that biddeth him God speed is partaker of his evil deeds" (2 John 10-11). "I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them" (Romans 16:17). "Him that is weak in the faith receive ye, but not to doubtful disputations" (Romans 14:1). "Follow peace with all men, and holiness" (Hebrews 12:14).
Clearly, there are two extremes to be avoided. One is the danger of being so narrow and intolerant that you create unnecessary divisions in the body of Christ. The other is the problem of being too broad-minded and sinfully tolerantso ecumenically minded that you settle for a shallow, false unity with people whom we are commanded to avoid or whose errors we are morally obligated to refute.
It would seem that the only way to be faithful to all the above commands is to have a sound and biblical understanding of how to distinguish between core doctrines and peripheral ones.
But search for serious material that carefully discusses biblical guidelines for making such distinctions wisely, and you'll come up mostly dry. This is an issue I fear most Christians have not considered as soberly and carefully as we should, and it would be my assessment that one of the crying needs of the church in this age of mindless postmodern subjectivity is a clear, careful, and thorough biblical understanding of when it's time to fight and when it's time to fellowship.
Few subjects interest me more than this. It seems a pretty obvious and foundational issue for the church and her leaders to settle. You might think the early fundamentalists ought to have done extensive work on the subject, but as far as I can see, they didn't. They treated several key doctrines as fundamental, based mainly on what happened to be under attack by the modernists, and they declared themselves devoted to "the fundamentals."
But they didn't always keep very clear focus on the distinction between what was fundamental and what was not. As a result, later generations of fundamentalists often fought and fragmented over issues no one could rationally argue were "fundamental." Predictably, the fundamentalist movement slowly collapsed on itself.
There are some valiant efforts currently underway to improve and preserve the best remnants of the fundamentalist movement. I sincerely wish them success. But it seems to me that unless the brightest minds and most careful theologians in that movement are willing to go back to this basic question and carefully think through the biblical and theological rationale for the original distinction between fundamental and secondary truths, certain things that ought to be clear will remain murky, and fundamentalism will be doomed to repeating cycles of failure.
If there's anyone left in the "evangelical movement" who is truly evangelical in the historic sense, the same thing applies to them, by the way.