There are 2 aspects of prohibiting illegal things!
1. As a matter of principle and as a law abiding citizen/company.
2. To avoid getting into a legal mess!!
Its the second aspect that most people are more worried about, mainly the forum owner (Digit) and also the admins (to some extent, even mods). So as long as they don't allow discussion about illegal things openly they have saved their necks and done what they "reasonably could do" to avoid it!
However, what people do privately can't be controlled by anyone. If not by PM, then by email! Whoever wants to do it, will do it anyhow!
Can you stop me from selling brown sugar from my home? May be you can, but you are not too bothered about it because you are not responsible for it. But if I come and start doing it from your home, you will certainly take steps to prevent that!
