I don't talk about this much, but I have Schizoaffective Disorder
. If I am feeling really depressed, I might not feel like having sex, but I wouldn't say it has affected me negatively. I was always highly sexual from an early age. I think the medications used to treat certain disorders can have just as much or more of an impact then the illnesses themselves. I've know people who've taken anti-depressants and had trouble with arousal or orgasm.
I am not saying mental illness doesn't affect sexuality. Depending on the disorder, sexual response could range from uninterested to taking extremely dangerous sexual risks. However, no two people are alike, and I don't think you can completely generalize people's sexual responses with mental illness.