Why was I called a racist?

Okay, I am 17 years old in high school. I am very outspoken and will speak my mind, im of irish/italian descent, from brooklyn and im pretty big 6'1 195 lbs. anyway a few times my "african american" teacher called me a racist, because during history class i said "blacks like to complain about their past, what about how irish and italians were discriminated against? why is that not in history books?" it went a step further after i broke up a fight between a black and white student and the black student called the white kid a cracker and i said "if you said that in my neighborhood you would not walk out alive, your real tough around your homies huh" and me and him were to fight and he shouted to "ur lucky your lil boyfriend was there to save u." he ratted me out saying i called him a racial name... what is this?? why are blacks always doing things like this? and why are irish and italians always made out to be the big bad racist inner city hooligans as they are stereotyped in movies. i dont understand this. we face the same isues as other white peopl