What are they so mad about?

Race, mostly, and then gender. They are scared. Many live on the economic bubble, making a living only because "others" are not allowed to do what they do, if not by law then by practice. Diversity is a plus-sum game, but that does not mean that everybody wins. New entrants in the workplace depress wages and, at least seemingly, get promotions as reparations.

The people who condemn these guys typically do not live with their stresses. That's why the men call their antagonists "elitists," people who can afford to give away other white men's advantages because they don't need them as much. That's what makes these men angry.

In a pinch, humans tend to fight rather than share. Self-selecting types can form co-ops, but, mostly, we return to Hobbes's war of all against all. The people who are actually losing advantages on which their sustenance depends are angry about that. Whether they "deserve" to be angry, or whether we should assuage their anger, are separate questions. We should, however, understand it and reckon with it.