it's tribalism, plain and simple.
is it all that surprising that with diabetics (well, at least type 1) being so few and far in between that we would want to elicit some sort of connection with any other person we hear of with the same condition?
I too, would not vote for someone because they are diabetic OR because of their race OR party affiliation OR hometown OR military record, but i would vote for someone because they are diabetic AND because of party affiliation AND hometown AND their favorite flavor ice cream AND their taste in art. AND. I'd support someone for the sum of who they are, and i'll admit, the fact that they were diabetic would add to that grand total.
it would be nice to think that we could make a decision based entirely on the particular skill/talent in question, but it's just not a reality. We don't live in a vacuum, and our opinion of the person in question as a whole is always going to play into who we support.
yes, the skill or their suitability for the role will always carry the most weight, but all the same we are always going to support the person we 'like' the most, and that person is always going to be the one who's beliefs/opinions/choices/lifestyle/tastes align most seamlessly with our own.
diabetes is a part of who i am, so inevitably it plays a part in who i choose to affiliate myself with.
all that being said, i don't actually vote in capacity but that as a citizen of my country, but i think the point still stands true.