"What is more likely: a racist becoming an anti-racist, or the vice versa?" Those who are opposed to racism may believe that the racist->anti-racist position-switch is more likely, whereas the racist may believe the opposition position-switch is more likely; I believe that those "may"s are in fact "likely", but I have no proof. However, let us suppose that it is more likely that a person with position X, being opposed to Y likely believes that humans are more likely to switch their position from Y to X. With such an assumption we can as the question, "why do people who assume that people who have position Y are irrationl/stupid/ignorant/evil for not switching to X?" The answer is provided by the term inferential distance.
When a topic is complicated, whether by technicalities (e.g. evolution) or by emotions (e.g. preferable behavior), inferential distance is that amount of understanding that must be induced in the listener before the listener will switch his/her position from Y to X, or from nothing to X. The greater this "distance", the more difficult such an induction will be, such that it might seem impossible ton convince the listener of anything. It would be an indefensible position to thereafter claim that the listener is irrational, stupid, ignorant, or evil for his/her lack of switching to X.
This in-defensibility is due to the fact that why one holds position X is plausibly irrelevant to the merits of position X. What is more likely is that the listener simply has not heard an accurate account of position X, thus rationally refuses to accept it; would it not be irrational to accept a position without knowing its assumptions and what it entails?
Look at it from the listener's perspective: suppose someone were to demand that you accept position Q; you respond by saying, "describe this position to me, such that I can understand it." He gives a short summarization of position Q, which amounts to no more than five sentences. With little to mentally digest, you tell him to sod off in a sort-of-polite manner. He calls you irrational for not accepting position Q, and you wonder why he is such a fanatical jerk; he must think that only his world-view is the correct world view. Thus, the viciousness of ignorance on both sides and of different sorts destroys any conveyance of understanding.
On the one hand, the man presenting position Q thinks you are [insert pejorative] for not accepting position Q, because he does not see that you need more information and more time to understand position Q before accepting it. In your case, you think he is a [insert pejorative] for his impatient demand that you accept position Q. These two failures are irrelevant to position Q; the messenger's virtues/vices cannot determine the merits/flaws of position Q any-more-than the personal peccadilloes of Bill Clinton affect his understanding of the concept of predication.
Well, maybe those might be related...
I hope you see what I mean, by this switching of positions in order to demonstrate the difficulty with convincing others to switch their position with respect to X, Y, or Q.