The sex section is the only one I delete stuff from sometimes without telling why or giving warnings, the reason being, there is so much stuff that doesn't meet the guidelines I just don't have time to PM everyone about it, and it's not a big deal where people need to be banned for it.
If you read the description of the section across the top of your screen when you're in it, it says
Sex in Marriage Sexual problems are common in many relationships. This section is for discussions about sexuality. Please limit discussions to those asking for help with a problem and those offering advice. Any other threads may be deleted.
Basically, anything that's not something where the person is asking for help with a problem, I try to delete it. The reason being, it tends to get too racy in there when people start discussing fantasies, etc. We don't want to attract that kind of traffic (people here just to talk about sex), because it ends up spilling over to the rest of the forum.
Not trying to indicate your thread was blatantly inappropriate at all, it probably just wasn't about asking for help with a specific problem you had.
Admittedly, I don't catch it all, and sometimes I leave stuff up when I see a bunch of people replied, and it stayed PG rated.
Hope that explains it.