I'm going to split a hair on the definition of "legitimate", because there are different nuances that take the discussion in different directions. "Legitimate" can be read to mean "logical and understandable", or "proper and acceptable". But these are not exclusive possibilities.
Consider the possibility that there is an inborn instinct to classify an unknown individual as "Of my tribe/pack" or "Not of my tribe/pack". Such an instinct is present in animals, and would likely have been advantageous to survival throughout the vast majority of human history.
I don't assert that it does exist (I'll leave that to the sociologists), but the existence of such an instinct would be a "logical and understandable" basis for racism. It would not, however, mean that racism "is proper and acceptable".
Yeah, so, I grew up in a very mixed race, international community. Quite a number of people of color are "of my tribe/pack" as far as I'm concerned, so race is not a differentiating characteristic on that point for me. And my base assumption is that people who are involved in and interested in sf are even more likely to be "of my tribe/pack"(despite the fact that, as you well know, there are members of the sf tribe who have severely hurt me. None of them were people of color, however). So I didn't say I don't have any "legitimate" reason to start into the discussion on a distrustful footing, I said I don't have any reason to start out that way, other than the sort of generic understanding that people can hurt other people.
Now, I do have a legitimate reason, especially based on recent experience, to believe that a fair number of sf-interested people of color might also have been exposed to academic and other fields of thought and culture that I *haven't* been, and so I fear misunderstanding them and being misunderstood by them. But for me that is different than distrusting the person. That is distrusting that we have a common language - distrusting, in effect, my own ability to translate my good intent into positive results. It is that kind of distrust that I think it is especially valuable to try to validate and then find ways to eliminate.