I completely agree Ana!
I'm fat... I know I'm fat... I don't pretend that any amount of costuming will make me not fat.
Being painfully aware of this fact, the few times I got into costume and went to conventions or masquerade parties I would either: A) dress up as someone fat so that my body matches the character I'm imitating or

dress up as whoever the hell I want (even though I don't match their physique and look more like the washed up, middle aged, overweight version of said character) but then not be phased by the looks or comments I would get... because I would be doing it for myself and no one else!
I have nothing against people not giving a shit and cosplaying a petite anime character even though they look more like Shamu the whale. As long as they are aware that their "interpretation" of the character is wildly off the mark and that people will usually say so. I hate people who parade their body around in costumes (and so, willingly expose themselves to other people's judgement) but then get offended when someone calls them fat even though they objectively are fat. If you are gonna expose yourself like that either be chill, relaxed and don't take yourself (and other peoples opinions) too seriously, or just toughen up, get thick skin and take it all in stride.
Beauty is subjective, not objective, so it can't be measured by any generalized, politically correct standard. A couple of centuries ago being fat was considered attractive... now? It isn't... in the future? Who knows!
In the meantime...