I think it would depend on the politician themselves and on the particular illness. There is no doubt in my mind that any politician declaring themself to have a history of psychosis, for example, would be committing, as you say, political suicide, but there may be more lee-way with other types.
If George Osborne published an article in The Telegraph tomorrow revealing that he has OCD, I don't think many people would have a problem with it. Or if Harriet Harman said that she had suffered from anorexia.
The real issue at the heart of the stigma is the often mistaken assumption that those with mental illness are incapable of rational thought, or cannot be relied upon, and bipolar disorder, depression, schizophrenia and personality disorders carry these stigmas in particular, I feel.
I've long considered a career in politics myself, and if I were to get anywhere with that I would be honest and open about my mental illness, simply because that's the type of person that I am. I feel it is a big part of my life and has opened my mind up to the suffering of others and increased my empathy in a way that perhaps those who have not been touched by mental illness, either personally or in the case of a friend or family member, has not.
Take the example of doctors - statistically doctors have a higher rate of mental illness than the general public. I'd have no problem at all with being treated by a psychiatrist with a history of mental illness, providing that at the time of treating me they are fit to practice, and therein lies the problem: the public are not trusting of mental illness, they do not fully understand it, as you rightly point out.
I think something does need to be done to put the wheels in motion though: the breakdown of the ignorance and stigma needs to start somewhere. Ideally, I'd say, with former ministers and MPs coming forward and saying "Hey, I was mentally ill when I was in this job and nothing went wrong", and as acceptance and understanding slowly spreads, current politicians might be able to do the same.
In some ways mental illness in the public eye is treated as a novelty or glamorised. The 'tortured genius' of Stephen Fry, Sylvia Plath, Robbie Williams. They are seen as people who have achieved
in spite of their illness, not as people for whom without 'mental illness' and it's accompanying insights and experiences might not have achieved anything.
It annoys me no end the number of people who still think schizophrenia means a split personality, not a split from reality, as is the actual origin of the name. It pained me when my mum told me not to keep in touch with anyone from the psychiatric hospital because they 'might be dangerous'. I don't want people crossing the street to get away from me, and I will never treat another person with mental illness in such a way.
The entire issue of stigma around mental illness needs to smashed to pieces because it is quite frankly sickening.
Sorry, bit of an essay there, but it's something that I'm really passionate about.