I'm probably going to get a lot of flack for this, and I might deserve some of it, but there's a very real difference between being "a bit hefty" and being obese. About 1 in 3 Americans is genuinely obese (I don't know the figures for other countries), and it poses serious health risks. It can, if fact, affect singing (lungpower) and instrumental music (manual dexterity). While it's certainly stupid for someone to assume you're a bad musician because you're overweight, I have little sympathy for people who have unhealthy eating and exercise habits, and don't take responsibility for their own physical condition.