There is a difference between being generously proportioned and being FAT. Some people are built big, and they look right big. They don't look FAT, they look in proportion and their flesh is firm and they don't have obesity-type health problems. Funnily enough they don't get that much discrimination anyway, because they look just right the way they are.
There are people who are overweight due to pre-existing health problems, which mean that they store excess fat & can't get rid of it. They are very unlucky, and I imagine they get a lot of painful discrimation which they don't deserve.
BUT - there are a lot of FAT people out there who are out of proportion - whose bodies are having problems maintaining and carrying the extra weight - who are eating and drinking to excess and not expending that energy due to sedentary lifestyles. They tend to be the ones that frankly don't look their best. There are people who are in denial about their weight and therefore wear truly horribly innapropriate clothes. There are people who are unhappy about their weight - so they comfort eat - so they get fatter - etc etc. There are people who are making themselves needlessly unhealthy and sluggish. Those are the people who need a wake-up-call, but they don't want to hear the message - so they try to hide behind the FACT that "not everybody who is fat is fat through their own fault". Well that's true - but its also true that not everybody who is fat HAS to be fat or is happy being fat. Its also true that "not everybody who is fat is unhealthy, weak-willed or unattractive". Again - that's true, but there are patently a lot who ARE.
So I don't think Gargoyle's harsh truths should be dismissed out of hand. And I think the realities of life are that FAT people will be discriminated against - because generalisations ARE going to be made. Being FAT shouldn't stop anyone singing - but you have to realise that whilst people may love your voice, they may not like your looks. That's their choice, and their honest reaction. You can either focus on what they didn't like, or focus on what they did like. FAT is not a sacred thing that we should all make allowances for. If you had a huge pair of ears and bottle-bottom glasses but sing like an angel - well you'd still have to expect that people will comment on your looks as well as your voice.
Anyway, and finally, have the courage of your convictions. I'd rather be a FAT singer with a beautiful voice, than a lean machine that couldn't carry a tune. Focus on the positive god-given gift, not the packaging. Don't cut off your nose to spite your face (ie - don't stop singing!) And if you don't like people discriminating against your weight, then all you can really do is to make an honest attempt to change it (but please do it sensibly and healthily - or you could lose the good things you already have).