Oh man, this is so difficult because there are so many social stigmas we need to throw out!
I think the main one that would get most of the things we need to get rid of is: stop trying to think that people need to live in a way that others approve.
This comes with difficulties of course because we also have a legal idea of what is allowed and what is not and you definitely don't want people involved in harmful behavior to others. But the idea should be: if it doesn't harm me or others why should I care how this person lives? I think the world would truly be a better place then.
Durkheim (the sociologists) looked at this btw and he sees the same difficulties: what we perceive as 'not normal' in our society will eventually become criminalized. So what is illegal doesn't say much about the actual behavior, but more that we as a society condemn that behavior. Take walking around naked for example. We have decided it's undesirable to do that so you would get fined or arrested if you did. But it doesn't usually harm anyone. This may not seem as that much of a problem since the group that wants to be naked all the time is not that large (or at least not that vocal about it). But if you were to change naked for gay, you get a whole other discussion and one with a lot of feelings attached to it. Because some countries think that that is fine and people should be attracted to whom they want, but other countries don't. So where is the line? When is a social stigma very harmful and when is it perhaps useful?