Mainly because they all argue that the movie portrayed him as a genius and a likable character? What movie were they watching? I didn't like the guy at all, but I respected his visionary sensibility and what he set out to do. Just because someone isn't likable doesn't make the movie any less good or interesting.
I have never understood the "logic" of the literal crowd, who can not seem to enjoy a film or TV show if they dislike the person(s) being portrayed on screen. Similarly with people who call a film "unrealistic" because it does not fit their limited and preconceived notions of life, ie none of their friends or family "act that way".
There are plenty of singers, musicians, actors, real life personalities that I strongly dislike as people, but still admire their work and talent.