There's a lot I could speak on with this subject, and to be completely honest, most opinions of this rank I typically don't share publicly as it causes unwarranted tension and friction. A good opinion once lost, is lost forever. That being said, don't read my post and start a fight over it. I'm more of a factual person then an opinionated one anyway.

That being said...

I don't know that there are many people in the world or in history who did not have a modern "mental illness." Before I continue, let me preface that I personally have a lot of history with mental illnesses. My mother was an actual sociopath, to an extent of also being a pathological lier. My older sister tried committing suicide at the age of 16 and in a desperate attempt to not take responsibility my mother had her committed to a mental institution where we discovered she had sever Bi-Polar disorder. My younger sister has ADD but is one of the most outgoing encouraging people you could meet. I personally have sever PTSD. After this period I worked as a caregiver at a special needs daycare where our primary focus was giving care to children with sever and minor mental disabilities, downs-syndrome children, handicap children, children with extreme allergies etc. Let me also state, the only reason why this is being stated is to give you a recount of my opinions, not for a pity cry or an attention grab.

Now, while there are many people with sever cases of mental disorders, I don't think it is something people should view so negatively. As my opening statement said. I don't think there are many people in the world or in history that did NOT have some sort of mental ability or disability. This is not a weakness, it's a personality. Yes, there are some cases where extra care and attention are required but, for the most part these mental states are just natural setbacks as most people have in any area of their life. Not everyone who can't spell has dyslexia. Some may not be the brightest, this does not mean they are mentally retarded. Some may be brilliant, this does not make them a genius, in fact many cases of brilliance can be traced back to mild-sever forms of ADD or ADHD. Please see Albert Einstein as a reference. 

Just as [@BrokenPromise] stated, people use these labels as an excuse for their behavior or to classify themselves with a group. Instead of fixing the issues they have with certain behaviors or circumstances, which can be done. I knew a little boy with autism who when he first came to the center was unapproachable, but by teaching him that he was okay, that it's okay not to be good at everything and in turn including him with the other children, etc, etc, I won't go to far into the details of this case, he turned out to be one of the kindest, most thoughtful children I've ever had the pleasure of meeting. He had a love more living creatures that I rarely see in any human being, mentally disabled or otherwise. Again, just because someone may have a disability it doesn't give them an excuse for their behavior. Do you think there have been no human beings in history without depression? Do you think they just threw down the hat and said, "Okay, that's it, I'm done." and just stopped everything? (these are rhetorical questions) There would be no history and no current if that was the case.

Okay now, on your statement about using RPG as an escape from reality, I don't think it is any different then playing a video game, watching a movie or TV show, reading a book, etc. Aren't all of those cases escaping from reality? So many people come home from a day at work and just turn on the television and close their mind off from the rest of the world. At least role-playing is a creative outlet, where people are bettering themselves in their writing ability and learning from the situations that come up within the role-play. It would only be considered "unhealthy" if like in any situation they ignored whatever was going on completely. Sometimes people have to wait out bad situations and given that time, would not want to spend the bulk of it dwelling on their poor state. If there were no outlets for bad situations, getting out of such situations would mean suffering for a time afterwards in a sorrier state then you would have been if you got your mind of it for a little while here and there.

Now, let the bitching begin. I'm ready.