Why do some white people get mad and say it was so long ago when black people bring up slavery?

I mean its was a couple hundred years of beatings and lynchings. Of course most people aren't going to forget that it happened.

Flagrant open racism only ended roughly 40 years ago anyways.

I'm not trying to make this into a race flamewar, I'm just interested in the minRABet behind it. I mean I hate black ignorance as much as the next man, but you have to understand that it somewhat stems from the culture that was bred as a result of slavery.