A quick guide:
Perfectly Acceptable:
Dating only the people you happen to be attracted to
Not Wrong, but Probably a Sign of Conscious or Unconscious Bias and Prejudice that is Worth Examining for Yourself:
Quietly filtering out whole demographics of people, in advance, from your dating pool and telling yourself it’s just a “preference”. (E.g. Trans people, black people, low IQ, ETC)
Bigoted and Problematic:
Loudly advertising those “preferences” in order to prevent one of the untouchables from mistakenly interacting with you under the misguided assumption that their “type” is worthy of a conversation or consideration.
|X|C|BDSM| 
Good and important observation. Thank you for that. Helpful, actually.