Hey,
Just wanted to add my thoughts...I'm trying to lose 2 stone 10lb, to get back to 9st 4, after years of being unhappy with my weight.
I'm spending a LOT of time in the gym and out running on the road, and as many have said here, I have nothing but admiration for people who are a bit on the larger side doing the same.
The only time I ever think 'why are you bothering?' is when people spend more time chatting than working out, especially in the pool, blocking the ends of the lanes, and it doesn't matter what size you are if you do that!!! I always think if you aren't putting the effort in what's the point of being there?
Anyway, the gym I use is a staff-only one where I work, and there are quite a lot of people who are probably 200lb+, just as there are quite a lot who are 'built like a racing snake', as one of my friends puts it, and loads who are like me, pretty average size with maybe 1-3 stones to lose. Everyone always just gets on with it (except the ones who stand in the shallow end and chat >.<) and if other people think like me, they're envious of the resolve of some of the larger folk, who are in there all the time, it seems like, and some of the people I see regularly you can see them shrinking from week to week. If only my ridiculously slow weight loss would take the hint!!
Good luck, and don't worry! You don't need to care what anyone else thinks or says, you are doing what is best for you, and there's no way anyone can knock that.