I also agree with you when you say that we should declare a truce in the culture wars. Amen, brother! Whether or not we can accomplish that goal is somewhat debatable. This raises the question, why would parties to a war want to declare a truce? The key reason, I believe, is if one could show each party to the war that they would be better off to cease the conflict than to continue it. With that in mind, why would each party to this war want to call a truce?
Liberals/progressives might consider a truce if conservative Christians would acknowledge that the science of Darwin, what conservative Christians have been fighting, is valid/correct. In a sense, that would offer liberals/progressives a form of victory. They certainly could claim a victory if it meant we stop teaching "junk science" in schools. So why might conservative Christians want to provide that victory to them?
I think conservatives could claim a "victory" in the following way:
1) acknowledge that Darwin and LeMaitre were right (i.e., evolution is correct and the Big Bang is correct)
2) out of that acknowledgement, however, make the argument that sin is a by-product of evolution (the argument I've been making)
3) if sin is a by-product of evolution, then humans cannot overcome their own sinfulness, so Darwin becomes a form of evidence that what Christians have been saying all along is correct (i.e., reinforces Biblical principles).
It becomes a form of intellectual jiu jitsu. In jiu jitsu, one uses your opponent's force against the opponent (at least that's what I understand, as I haven't studied jiu jitsu). In this case, Christians use the force of the argument about evolution against non-Christians in the following way. Christians can say, you non-Christians are absolutely correct about Darwin and LeMaitre - some of we Christians have gotten that wrong up to now - but we are taking your arguments about Darwin and turning them around to make the point that they actually reinforce what we Christians have been saying all along (i.e., that mankind is inherently sinful and cannot overcome that sinfulness on our own).
Thus, each side can claim a form of victory. Liberals/progressives can benefit because we can end this argument about evolution and the age of the universe, and conservative Christians can claim a victory by the argument that it reinforces what we've been saying all along about the Bible.
However, with respect to conservative Christians who've resisted Darwin, there won't be movement unless and until they feel they've gained something. Unfortunately, the strategy we've largely pursued to date - that Christians should accept the science because it's good, and it doesn't contradict the Bible - provides them no gain, at least not in their minds. The science can be right "all day long" but it doesn't give one a reason to change his/her mind. That's why I believe if we really want to have a wholesale change in conservative thinking on this subject, we have to provide YEC's, OEC's, and ID proponents a reason they should WANT to change their minds.
Now I'm confident that even if we reach a detente about this issue, we'll keep arguing about something, probably a bunch of things, but we'll at least stop arguing about this.