Uhm, I'm going to contribute to the topic, but can I just say first that as someone who was diagnosed with Aspergers by a professional as a small child that I don't consider myself to be mentally ill? I have an neurological disorder that sometimes inhibits the way I function socially, but I am perfectly sane, and in fact, I have always scored higher then the average person in tests of empathy. (Which means that whole stereotype about us not having empathy is bull.) I'm not trying to start a fight with anyone, but I thought it would be helpful to clarify with my own life experiences. 

People faking Autism on the internet (not accusing anyone here, I don't consider that my job to judge without knowing) is very hurtful though, especially since I've gone through my whole life never asking for pity from anyone, just to be treated like an equal, and yet other people use it as a way to get attention. It also makes me feel like no one will believe me if I tell them I have it, which is why I always go out of my way to clarify that I have a diagnosis from a doctor. I'm not trying to find people who will treat me differently, I'm trying to find people who will treat me [i]the same.[/i]

Now that's off my chest, I mainly believe with regards to this the same thing I do about all controversial topics- you just have to be confident as a writer. There are no 'bad' ideas in writing, only inexperienced writers or under researched characters. Mental illness is never something we should avoid talking about, because those people are still human beings and they deserve to be part of our stories as much as anyone else. In fact, be it fiction writing or an internet RP, it's important to discuss controversial topics because that's the bane of ignorance. Still, research is the most important thing, and not just fact-checking on Wikipedia but actually going out and having real life experiences with the topic you're talking about. Fiction is a reflection of the writer's reality, and to write whatever your heart desires, that's all you really need to know.