It's easier to say "no swearing" then to say "OK, you can swear, but only when you use the words in this context and against these people and you can never say these words cause they're too bad and this this this.... etc"
Yes, many of us are probably mature enough to use this well. But many of us probably aren't, not to mention the people who don't read the forums anyways. It's much less work and hassle to just say "no swearing at all."
