You were 2 when Nicholson's Batman movie came out, so I imagine you read that there was a lot of anger and rage over his casting, not experienced it first or even second hand. Remember the internet wasn't common or heavily used back in 1989, so any anger had to have been localized or the rantings of movie critics in magazines. I guess people who write about it now are just reminiscing about their own feelings from back then.
People will never learn to not judge a book by its cover. It's why beautiful people will always be more successful and coveted than less attractive ones.
It did just fine in the box office, making $48million on opening weekend, $202m lifetime domestically, and $375m worldwide (http://boxofficemojo.com/movies/?id=batmanbegins.htm) and spawning 2 more (soon to be at least a third Justice League movie) successful movies.