Yes you can have preferences but it’s about the tone. Saying “obviously not attracted to them, never in a billion years” is an extremely distasteful way of sharing your preference. And it’s quite different when it’s a group of people who have been treated as inferior humans in the not-too-distant past. A more analogous comparison would be to replace “black” with Jewish in this example. If someone said “I would obviously never be attracted to Jews, never in a billion years”, it mirrors negative sentiments that were in place very recently in history. They could’ve said instead “I prefer to date someone who is white/Christian like me” and that suddenly makes it less about a group of people and more about you/your preferences.