I agree the warnings are sometimes OTT and the need for them could be alleviated by more specific thread titles. Subject lines like "How do I handle this?" and "What would you do?" aren't very helpful.
Increasingly, though, just because a distressing topic isn't in the OP doesn't mean the thread is safe. We have had domestic abuse, molestation, pedophilia, emotional disorders, physical violence, self-harm and other heavy-duty topics interjected into threads that started out as fairly benign etiquette questions. I know I'm not alone in finding it very disturbing to come to what is essentially an entertaining message board and be exposed to members' issues of the sort that require professional assistance. There is little to nothing anyone here can do to help Internet strangers with serious dysfunction, mental health matters, abusive spouses, profound depression, etc. (I'm not talking about the hugs folder, where more personal matters seem generally acceptable, and which can be avoided by those who don't want TMI, but threads in the mainstream forums)
People might want to pause and reconsider before they post, say, "Thank-you notes are a very unpleasant topic for me because I was once forced to write a thank-you note to the neighbor boy who my parents were unaware molested me," thus spinning the whole thread off into a discussion of a terrible and heart-wrenching topic instead of the writing of thank-you notes. Some people find it very upsetting to be skimming along in an on-point thread only to come across a tangentially related horrible episode someone suffered in their past. I feel bad for those people and realize it is helpful to get things off of one's chest but understanding the right time, place and audience for baring one's soul is a big part of adopting proper public behavior.