Just like car forums and the like the user takes a risk. The user has to deem himself capable of the job he's going to undertake. I agree that there are certain liabilities but with the proper disclosure those liabilities are released.
Not to mention it's relatively easy to tell who knows what their talking about vs. Some Joe who feels like he can fix it.
It's a grey area but if it comes down to me I would help union and non-union members alike. It still takes skill and know-how to do a job. Being on a forum and asking questions isn't going to fix everything. But it helps point someone who knows where to look in the right direction.