Homosexuality and bipolar, aren't comparable. However, there is something behind what you are saying.
Looking at bipolar from the social model of disability perspective, the social attitudes towards your illness/condition are the bit which is disabling. Social attitudes might not account for everything which is shit about having an impairness, illness or long term condition, but they sure as hell make it a lot worse.
By comparison, I have anxiety disorder and OCD. Medical treatment - CBT and anti-depressants - has helped a great deal. However, what has helped just as much is the growth in confidence and self esteem I have experienced from learning that many social attitudes around my condition are incorrect. Eg, I may occassionally have panic attacks or be slightly neurotic but that doesn't mean I am incapable or can't be trusted. Moreover, my compulsive thoughts do not make me a "monster" or an evil person.
Equally, for many gay, lesbian and bisexual people, life got better when they - and society at large - started to recognise that that social attitudes and not homosexuality itself was the problem.
So yes, to some extent I do see what you are saying, and I do believe that the social model can be very empowering. That doesn't mean that an actual mental illness and a sexual orientation are comparable - it just means that society can learn from how it has made lives better in the latter instance what it can do in the former (indeed towards all disabled people).
I also don't think that the social model is a fully cohesive and all-encompassing explanation. Frankly, (using my personal eg) society could be supportive and tolerant to the back teeth and it would still be shit and it would still be an illness for me to stop shaking in a cold sweat in the middle of the street because I am overcome by a compulsive thought that I'm going to harm my dearest loved ones. However, recognising that the DSM/medical diagnosis aspect is only one part of the issue is very important.