The Bernies of the world likely have no opinion on billionaires. (I'm sure you've all noticed that the socialist's screed went from millionaires to billionaires once Bernie himself became a millionaire, but I digress.)
Railing against billionaires and millionaires is for their base to get enraged about.
That's it. It's a way to fire up the ignorant.
It doesn’t fire up the ignorant, so to speak. It fires up the over-educated who feel undercompensated. All those people with Master’s degrees that are useless and can’t get them a job that pays better than a filing clerk at the DMV. THOSE are the people who buy into resentment.
So yeah, maybe they are ignorant. Overly educated but still ignorant.