Is it wrong to judge how people behaved in the past based on today's morals?

Someother lad: Does the fact that the masses regard something as "the right thing" make it the right thing?

You: If by "masses" you mean the absolute majority of the population, then yes.

Whether or not you personally think fascism has been disastrous is irrelevant to what is good or bad. It's the evaluation of the masses that decides per what you say above.