I guess it all depends on what your priorities are.
First, threads in the regional drug discussion forum are basically bluelight's acceptable sourcing threads. People discuss what neighborhoods to buy their heroin on, when in other places on this site even maps of drug crime activity have been considered unacceptable. (I haven't read all the threads, but I'm talking about the chicago one, where posts like I've described have sat around for years now, so I don't think this is a fluke?)
Second, I don't know how accepted it is, or true, or just my impression, but it seems like a large part of the social forums consists of 'hey lets meet up and take x drugs'.
So the implicit separation of the two forums seems to make sense if bluelight wants to keep the Harm Reduction persona up.
However, I think that merging the two fourms would provide a great way for druggies to meet each other and create trust for pm's to trade connections and stuff like that. And that would make the forum a LOT more popular, I think you could almost expect a rush of new posts and posters. And it would be 'real' harm reduction in terms of reducing the amount of danger in scoring the drugs (with an increase in police awareness? I dunno)
However, like I said, making a forum for social discussion of regional drugs seems hard to justify as 'harm reduction' like I understand it with the current rules.