I would say that yes, they should be allowed, on some conditions: Firstly, the locale of the question is clearly defined (USA state by state, USA national, Micronesian, etc). And secondly, that it's made clear, by asker or answerer, that the internet isn't the final authority on legal matters, this is not advice from a lawyer (unless it is), and so on. I understand the minefield of issues surrounding these sorts of questions, however often there are no other resources, and I've found that often I'm left with two choices: ask the SO community, or pay my lawyer my months wages to answer it.
Laws and robotics are clashing more and more - self driving cars need to be licensed, and, perhaps a better example, is the issue of flying drones. Drones could, in the immediate future, become the target of many laws, including privacy laws and the concern that they could easily fly a weapon to a target autonomously. Hobby robotics has become large and powerful enough to warrant attention from the law, and I believe that to ignore the issues of legality, especially when there are so few other places to get answers, could do the community a grave disservice.