Except that saying someone could be "missing out" by ruling out sexual relations based on genitalia is essentially the same as when people tell homosexual people they could be "missing out" by ruling out sexual relations with the opposite sex. In both cases, "ruling out" people has to do with what the individual desires in terms of sex and intimacy...it isn't a matter of feeling hatred toward other people as human beings.

Whether you call it "preference" or "bias" -- why is it such a big deal to you if someone else is "missing out" on what you believe could be a fulfilling relationship for them? Isn't their (hypothetical) loss somebody else's gain?