diabetes definitely shouldn't be a disability. neither should HIV, obesity, etc.
the overwhelming majority of HIV cases in the US are self conflicted or participating in an act where you know its a consequence... same with obesity, for every 1000 fat people probably 1 have a legitimate thyroid problem... the other 999 only have a thyroid problem cause they eat way to damn much. i know quite a few people with diabetes whose work it doesn't effect, i'm sure there are some extreme cases, but most people live with it fine and control it with insulin and diet.
really, if its your own fault you got something (fat, full blown aids, etc.) or something you could easily work with (diabetes... most bi-polar cases if properly medicated), then it shouldn't be considered disability.
especially since HIV is just the infection. you could make a lot better argument for full blown aids where the immune system is simply shot and they shouldn't be around people...
Diabetes is a disability. As is obesity.
A virus is not.