No, jno, sincerity isn't everything but there are huge differences between Robespierre and Hitler. For a start, Hitler used his power for personal benefit, he courted business leaders to boost his wealth and even used his own name in his party's salute..very different from the more modest Robespierre. Secondly, Hitler's policy from the outset was the elimination of Jews and the preservation of an Aryan cultiure, Robespierre's was the good of France. Hitler advocated violence from the start, Robespierre was drawn into violence reluctantly.
The issue I mainly have is with the question: it's debatable whether he was a villain of the revolution. For a start, the question implies that the revolution was a bad thing, questionable in itself. Secondly, was he the worst 'villain'? That's even more debatable: it was Danton who created the Terror, Robespierre found himself drawn into it.
I'm not claiming that he was some sort of hero but I think that he was bascally a decent man who found himself in a situation that he couldn't cope with and resorted to acts of evil. History judges him badly as the pro-Dantonists wrote the history. Britain's opinions were shaped by Carlyle's hostility and the process was completed by fiction writers such as Buechner and Dickens. As I said, I think he gets a bad deal.