Maybe it´s just me but I get the feeling that more and more people seem to be interested in sex than BDSM. Even on websites about BDSM it seems the main topic is sex. It usually starts subtle with people looking for other people but it often comes down to people that look other people for sex. But it doesn´t stop there, people want to know how many times you´ve had sex and what your most kinky spot was to have sex. So I guess it is all about sex....
Of course there´s nothing wrong with sex, but I think there is a time and a place to talk about such things. I don´t think that the first post in a group for BDSM is that place! Sex is important in a relationship but it shouldn´t be the first thing you talk about when you meet someone, especially when the other person is a stranger. Which is why I´m a bit suprised how open and honest (assuming that people tell the truth) people are in such topics. Maybe it´s a cry for attention and it could also be a way of finding other people, but I don´t think that this is the best way to do so. There are far more subtle ways of getting the attention of someone without having to talk about sex.
So when should you start talking about sex? Well that´s up to you, I mean there isn´t really a rule for that and I don´t think you can make a rule for that. But I don´t think it´s something you talk about when you hardly know someone. Unfortunately people are often more obnoxious online and that usually means less civilized behaviour. When I want to get to know someone then sex isn´t really a topic I talk about, because it´s not something that I´d be interested in talking about when I don´t know someone that well. Wouldn´t you first want to know the favourite movie of someone or what his or her job is? That seems to be a bit more interesting and it´s less invasive, because talking about sex with someone you barely know could be considered as rude and might have a negative effect on the conversation. If you really want to bring it up then I would really suggest to wait with that, because it´s not something everyone feels like talking about with someone they don´t know. Maybe there are exceptions but most people are often not that open about their sex life!
If there is a mutual attraction then the subject will come up sooner or later, but once again I wouldn´t rush things. People that have to talk about sex already in the first ten minutes of a conversation usually sound like a desperate case, even when you´re not some people might take you for one. I don´t think you want to be seen as a desperate case and even if you´re one I doubt you want to be seen as one, so take your time and talk about other things. Show some interest by asking about what they like or what they do, try to be original with your questions and you might actually get the attention of someone. That´s hardly ever a bad thing!