I guess most people accept that the statement "I am not racist but " usually comes before a very racist remark.
But I have noticed another phrase common on here
"I'm not racist, I just don't like "
Why is it similar? Because you can't really know why you don't like someone. You may think it's a rational dislike, but all the evidence is that it's actually an unconscious decision on top of which you add rationality.
All the evidence? Because BAME people know they are more likely to be disliked / police searched / lose out at interviews than white people. Because we know that people who are chosen in blind tests are not chosen if the tests are not blind, no matter how unbiased the people doing the choosing think they are.
It's really difficult, and it is hard / daft to attribute to individuals a behaviour that emerges from people on average. And most people want and try to be non-racist
But when a BAME person suspects that racism underlies something, denying that , which happens on here, or claiming "not me" seems a very racist thing to do.