I think the biggest problem is assessing the knowledge of the person posting the question.
In a few cases, the question reveals enough about the person to demonstrate that he obviously knows so little about the subject that he really should not be tackling the project (I don't think there are many that fall into this category here -- They're probably at the "How to..." sites).
Other times the original question may sound reasonable and we might answer in general terms, but a follow-up makes it clear that the person has not understood or obviously has insufficient knowledge or skill to be messing around with his wiring. At that point, it is probably prudent to say, "Sorry, but I think you're getting in over your head and should seek professional help."
In this last case, we may even save somebody. If he had received no advice whatsoever, perhaps he would have just gone ahead and tried anyway. If he receives answers which make him realize that he's way out of his depth, then it just might
stop him from making a dangerous mistake.
I don't see a problem with answering in general terms. Despite the fact that common sense seems to be a vanishing commodity these days, I would like to believe that most people asking a technical question on a forum such as this have the sense to realize that without actually seeing the installation we cannot take into account every possibility and allow for every problem that might occur.
It's a hard decision, but I think we just have to take each case on its own merits.
Disclaimer: Views expressed in this message are entirely my own. I am not responsible for any misapplication of any information I may or may not have provided. If an asteroid crashes into the earth next year, I'm not responsible for that either.