I'll throw in my two cents:
The white Leftists (I don't call them "liberal" anymore) are in actual fact those who truly hate blacks, gays, and other groups they view as inferior. Maybe hatred is the wrong word and "contempt" is a more fitting word. In the case of blacks, they feel that the blacks are so inferior, that the only way for them to succeed, is to tip the playing field in their favour. So they give blacks advantages, so they don't have to feel guilty when the blacks don't succeed. They will never criticize blacks because they think that they are beneath criticism, which is a horrible opinion to have about any group of people, when you think about it.
Also the Liberals have this idea that since all people should be equal, that somehow makes all people the same. They don't recognize that there is a difference between equality and sameness. So they will convince themselves that blacks are the same as whites (though they have very different cultures), women are the same as men (though they have very different minds), all religions are the same, and other ridiculous things like that. This has led them to ignore at any cost the differences between people. And therefore, admitting that there are serious social problems within the black community, becomes an act of racism. They will never do that, and will condemn anyone who does.
And yet, there are blacks such as Ward Connerly who recognize the social problems within the black community. For whites to look the other way (despite what the Leftists think) is not an act of tolerance. It is an act of contempt. If those on the Left really loved minority groups, as they claim they do, they would hold them up to the same standard of behaviour as everyone else.
Maybe those on the Left are trying to lower standards generally, so they can feel good about their own failures.