In light of Cruz endorsing Trump, I'd like to make another point. This is not about the ethics of voting for Trump in the general election. That's a separate issue.
Rather, it's about the social psychology of moral compromise. Moral holdouts are despised because they make everyone else look bad. Suppose you have 20 moral holdouts out of 100. That's tolerable. For one thing, the 20 moral holdouts support each other. They may be a beleaguered minority, but they have each other. And they other 80% feel that their majority status validates their views.
Now, you might think that as the percentage of moral holdouts declines, they'd be easier to tolerate because they are so increasingly insignificant. Their numbers are too low to wield any power.
But in reality, the fewer the moral holdouts, the more intolerable the remaining moral holdouts become. They make the defectors to the majority look like cowards. And they make the majority look bad.
They stick out. As their power diminishes, their moral authority increases. Everybody else looks morally compromised by comparison…because they are.
There is, therefore, extirpative hatred directed at the moral holdout. If only he'd give in, then everyone else could feel good about themselves. But the very existence of that solitary moral holdout is a tacit judgment on everyone else. They can't stand it. So there's crushing pressure on all sides for the moral holdout to knuckle under and join the club.