Choice
We have a lot of rules governing the discrimination or non-discrimination against certain groups. Many of the rules that allow discrimination against homosexuals are based on the premise that homosexuality is a choice. If so, why are the following allowed exemptions:
Pregnant women - in these days of abortion, birth control, and adoption, no woman needs to be pregnant or raise her child. Why are pregnant women permitted rights in society that others are not?
Veterans - the draft hasn't been in place for about thirty? years, meaning we have a generation of vets who volunteered for service. They chose to go into the army, thus they chose to put themselves in mental and physical danger. Why should they be treated differently? Even those who were drafted could have chosen not to fight.
Religious people - even if one is raised is a cult, one has the choice at a certain age to get out of that cult, get out of religion. Yet if one is religious, one is able to do all sorts of things...special holidays, special weapons, special dress...that others are not. It is also totally unacceptable by modern standards to discriminate against any religion. Why? Religion is a choice.
Interracial marriages - People choose all the time to marry in their own race. They don't have to mix with those of other races. They can do well in their own gene pool and stay out of that of others. Why are these allowed?
Just a few small examples. I don't believe any of them, even the religion one (oddly enough). But society regularly rewards people who make decisions to do things that inconvenience themselves or other people. Why? One could argue the necessity of pregnancy (until we get that womb machine) or military service (ditto, only replace womb with war), but what about the others?