There are a number of very good reasons to be against it.

First, chances are none of us are trained experts in the field of mental health. As a result, the advice we give may be well intentioned, yet terrible. A thread like this could provide solutions which simply exasperate the problems, making things worse than they already were.

Second, even if we expressly state "this is not a substitute for a professional," there are people who will inevitably take it as such and pass on visiting a licensed doctor, or at the very least delay it.

And all of that's assuming well intentioned advice is given out. The thread seems just as likely to be overrun with trolls (see the relationship thread) and be turned into an absolute joke in a day or so that likely just makes people feel worse about themselves than when they started.

Yes, there are many potential risks, but I think you may understate just how much something as little as somebody to talk to helps. If there's people on here who are willing to talk to people who may be suffering from loneliness or something like that, it could help greatly.

A thread could also identify that point and urge people to get help. 

It's a fine line between genius and insanity, and I cross that line frequently. But I would not disclose personal information to strangers on the internet. I will however take out life's frustrations online by cramming a blue shell up someone's behind in MarioKart.

Well, maybe there are some people who just want somebody to talk to, even about everyday things or hobbies, instead of necessarily declaring their issues.

I nominate Rolstoppable as VGC Official Psychologist.

His prognosis would get a combination of "I'm better than you" and "get fucked".

Well if people ever need help, I can offer my fine services for $100

No refunds

lol $100? You are one cheap ho.

...

Where do I sign?

Actually, I have no idea what you're referring to! I just wanted to do something positive on this site.