I have trouble understanding their groupthink mindset.

It's a mass hysteria.

Let Mark Twain explain it to you:

It is thought, as I have said, that a lynching crowd enjoys a lynching. It certainly is not true; it is impossible of belief. It is freely asserted--you have seen it in print many times of late--that the lynching impulse has been misinterpreted; that it is act the outcome of a spirit of revenge, but of a "mere atrocious hunger to look upon human suffering." If that were so, the crowds that saw the Windsor Hotel burn down would have enjoyed the horrors that fell under their eyes. Did they? No one will think that of them, no one will make that charge. Many risked their lives to save the men and women who were in peril. Why did they do that? Because none would disapprove. There was no restraint; they could follow their natural impulse. Why does a crowd of the same kind of people in Texas, Colorado, Indiana, stand by, smitten to the heart and miserable, and by ostentatious outward signs pretend to enjoy a lynching? Why does it lift no hand or voice in protest? Only because it would be unpopular to do it, I think; each man is afraid of his neighbor's disapproval--a thing which, to the general run of the race, is more dreaded than wounds and death. When there is to be a lynching the people hitch up and come miles to see it, bringing their wives and children. Really to see it? No--they come only because they are afraid to stay at home, lest it be noticed and offensively commented upon. We may believe this, for we all know how we feel about such spectacles--also, how we would act under the like pressure. We are not any better nor any braver than anybody else, and we must not try to creep out of it.

They're actually not out for blood, only a few people even want that.

Most are just cowards who are virtue signaling that they are good people to their social clique.

Lynchings are the final form of a virtue signal.