It takes more than a couple generations though to cure all discrimination, and the aftermath of slavery is still seen in ghettos in every major city, the results of ethnic cleansing are seen in reservations even today, etc.
Some have known through all of human history that people are just people, but you only have to look back a couple hundred years, and you'll see the majority of people really did believe that some people were more equal than others.
It's very naive to think no remnants of that remain in our collective conscious, people don't change that fast, no matter what genetic science, common sense, and basic decency tell us.
Is it fair then to "discriminate" against white people? Of course not, the problem is, people tend to see discrimination in nothing but what is really equality when they are used to being "more" equal.
You can see it in comments like "I guess crippled people have more rights than me," - one man's response at a town hall after a lady in a wheel chair was allowed to ask a question... which he heckled. What he didn't see was people he agreed with were allowed to ask questions as well. His voice was heard as much as hers... but because she was allowed to say anything at all, he saw that has him being discriminated against.
The point being again, people see discrimination when the playing field is simply being leveled, when they are used to being more equal.
So it takes some thought. It is certainly possible to go too far the other direction. But all of the poverty numbers, graduation statistics, prison statistics, and the faces of those who represent us compared with the faces of the general population, tell us pretty conclusively that we still have a long long long way to go before this "past" discrimination is really the past.
Let me ask you, since I'm assuming you roll in much more Conservative circles than myself, how many times have you heard our first black president was only elected because he's black? That it was somehow "white guilt" that got him elected?
I have heard it dozens of times. Why would it be so hard to believe a black person became President, and it had nothing to do with him being black one way or another? Why is it is hard to believe the majority of people simply think he's the best person to lead this country?
Whether one personally thinks he's the best person to lead or not, it's hard to argue he didn't win by a whole lot. So why for some is it about race?
Now that's the President. Do you think every minority or woman CEO, boss, or generally successful person doesn't have this significant number of people saying "they only made it because they are black/Hispanic/have tits, etc." ?
Discrimination is very much alive unfortunately.