Hey nice white people, stop giving disclaimers that you aren’t racist—it feeds the ironically racist assumption that most white people are racist.
There are generally two situations in which someone declares that they are not racist. The first is when a person is about to say something racist, but they want to get away with it. It usually goes like this: "I’m not racist, but...." And, then, they proceed to say something racist. It is clearly a cop-out, and perhaps, even a lie. Claiming not to be racist doesn’t give you the right to make racist comments. Nor does it change the content of those comments to somehow make them not racist. In short, comments stand on their own. Claiming not to be racist, right before saying something racist, is nothing more than a lie. We should judge these people accordingly, as both racists and liars.
On the other hand, there are times when a well-meaning person, treading close to a controversial issue, may feel obliged to give a disclaimer. It may be a discussion of the lasting impact of slavery on the I.Q. scores of black Americans. Or, it may be a discussion of whether Hitler’s actions were successful at increasing the transmission of his genes into the future. A well-meaning white person, who knows that these topics include arguments used by racists and white supremacists, may feel tempted to give a disclaimer, in order to show their distance from such assholes (despite the similarity of their skin color to the members of those groups). Basically, they want to show that they are "one of the good ones."
Consider a black person entering an intellectual conversation, with a disclaimer that they are "one of the smart ones." "Now, I know that I’m black, but I want to let you know that I have a Ph.D." Obviously, such a statement has no bearing on the quality of one’s arguments, and is thus unnecessary. More importantly, it validates the assumption that blacks are uneducated. But, this assumption should be challenged, not validated.
Disclaimers of these types are unnecessary— and, ultimately, counterproductive— because they validate racist assumptions. It is a huge mistake to assume that a white person discussing the science of race is a racist. In fact, it is a racist assumption. White people should not be baited into addressing this racist assumption. Signaling that you are "one of the good ones" implies that most others are not. If you discuss topics respectfully and rationally, then there is no need to give a disclaimer. Again, comments should stand on their own as racist or not. It doesn’t help to validate the assumption that most white people are generally racist. Should this assumption rear its ugly head—perhaps in the form of an accusation that whenever white people talk about the science of race, it is because they are racist—then you should reprimand them for espousing their own form of racism. You certainly should not validate the racist assumption at the outset of a conversation, by labeling yourself as one of the not-racist whites.
We should be able to discuss controversial topics without inviting unfounded accusations of prejudice. There are scientific facts about race and about the relative success or failure of Hitler’s genes. Those facts are what they are, and they are not going to change. We have to be able to talk about facts, regardless of how others have distorted them for propaganda. Unless someone says otherwise, we should give them the benefit of the doubt and assume that they believe slavery, Jim Crow and the holocaust were bad things. If people can’t tell the difference between respectful conversation and racist propaganda, that is their problem.
No one should assume a person’s opinions based on the color of their skin. If your speech and behavior is respectable, then it should go without saying that you are not a racist asshole. And, it’s kind of pathetic, if you feel the need to preemptively address such racist accusations. "We should be able to discuss controversial topics without inviting unfounded accusations of prejudice."