I'm going to go against the majority here: yes, it's wrong to make that assumption in any circumstances where you would actually need to.
What I mean by that is: when I meet someone, their sexuality is usually completely irrelevant to my interaction with them. I'm not 'assuming' they're straight (although obviously if called on to make a guess, I'd guess that they were, since that's the most likely option), I'm making no judgement on the subject one way or the other.
At the moment when the question becomes relevant (eg, when asking if someone has a partner), I think it is a little bit rude to assume they are straight, and it's better to word the question in such a way that it doesn't prejudice the issue either way. So 'are you in a relationship?' is a better question than 'do you have a girlfriend?'. Not that I think anyone would be offended either way (I did say 'a little bit'!), but it's good training, a reminder to yourself that yes, statistically there is a more probable answer, but it's not the only possible answer.
It's the same argument as saying that, if you're talking about a generic nurse, it's good practice to say 'they' rather than 'she' until you know for sure, even if 95% of nurses are women (or whatever the actual figure is).
What I mean by that is: when I meet someone, their sexuality is usually completely irrelevant to my interaction with them. I'm not 'assuming' they're straight (although obviously if called on to make a guess, I'd guess that they were, since that's the most likely option), I'm making no judgement on the subject one way or the other.
At the moment when the question becomes relevant (eg, when asking if someone has a partner), I think it is a little bit rude to assume they are straight, and it's better to word the question in such a way that it doesn't prejudice the issue either way. So 'are you in a relationship?' is a better question than 'do you have a girlfriend?'. Not that I think anyone would be offended either way (I did say 'a little bit'!), but it's good training, a reminder to yourself that yes, statistically there is a more probable answer, but it's not the only possible answer.
It's the same argument as saying that, if you're talking about a generic nurse, it's good practice to say 'they' rather than 'she' until you know for sure, even if 95% of nurses are women (or whatever the actual figure is).