Reading historians, and especially anthropologists, it is easy to see why they tend to be very liberal in their politics. Their identification with Western civilization in general, and America in specific, is counteracted by their identification with other cultures. I don't mean that they necessarily favor other cultures over ours, but national and cultural loyalties are weaker for them. Our country perceives itself to be in danger and wishes to go to war; they can instantly name a dozen other cultures that felt as strongly about defending their way of life. Because all times and places have their loyalties, they see loyalty as a constant, and all loyalties as somewhat equal. Because New Guinea tribesmen or minor Celtic kings got all worked up about their own power and influence, they see American aspirations as little better.
They consider it their job, in fact, to point out to the rest of us how unspecial we are. With that as a mindset, it is easy to see why they would reflexively oppose wars - don't all nations feel justified? Doesn't every culture try to use its religion to support its secular aims? Didn't the Mongols equally believe they were worthy of conquering others? Also, they often adopt a cultural neutrality in their professional work in order to better understand a culture. They train themselves not to conclude too quickly that something is good or bad. Therapists, another batch of liberals, do much the same professionally.
Because it is their cast of mind professionally, they easily gravitate toward believing that this is a good way to think generally. That's rubbish, of course, but it is the rubbish of certain educated people decade after decade, so it's worth taking into account. They are not going to stop thinking like that. People in the social sciences are going to believe in social equivalence, no matter how ludicrous it seems.
We, however, can step back from them a bit and observe them from the outside, much as they observe the rest of us. They delight in going against the common wisdom, seeing good and usefulness in things we call evil, and pointing out that what we call good is evil from another perspective. Unless you have done this type of thinking yourself, you can't know how delicious it is. To see what others miss! To understand what others dismiss! It is so ubiquitous in these fields that the participants no longer see it as a type of thinking. Does a fish know it is wet? They believe it is Real Thinking, which they can do and others only attempt.
Because they know all the black hats and white hats are actually gray, they become unable to distinguish between shades of gray. If one carries that thinking to its extreme, there is never any cultural or moral progress, only change. They don't actually believe that in their heart of hearts, of course. They have strong opinions about what constitutes a good society. Cultures that treat social scientists as special people and fund them generously are good societies, for example. Cultures that believe in moral equivalence in matters of sex and religion are good societies.
Just for fun, let's take an opposite view as better for mankind in the long run. We should always root for the side that is 51% righteous against the side that is 49%. No dithering, or apologies, or faintheartedness: if country A is slightly more humane, generous, intelligent, whatever, we should assist it against country B. Even if A wants to wipe B off the map, we should be on their side. Eventually, we would all be better off, right? Four, five centuries of this and we'd be a better people.
It sounds like a shoddy morality to us because the percentages are so close. But this is in fact how Western Civilization has moved forward, and brought us to a place where lives are long and few citizens are absolutely wretched. We can usually do better than 51% morality if we look for it - the northern states versus the southern in the the 1860's, for example. If we required then that we wait until one side is the 80% moral one and the other 20%, we would never have freed the slaves. Real people and real cultures never get to that superdominance in morality. But rather than being a reason not to go to war, as social scientists think, perhaps it is actually a justification for some wars. The enormous human cost makes marginal moral gains not worth it. 51-49 is out, then. How about 60-40? 70-30?
It is legitimate for those who greatly oppose wars to try and push the requirements as high as possible. But those who live under injustice think that it might be justified at 51%. Certainly, there is a point at which it is a sin not to eliminate the evil.