Well you would be amazed what size things come in, when shopping ebay for skirts I ran into tons of very very short mini skirts up to size 3x. I have no problem with people wearing what they like if they are comfortable in it and can pull it off more power to them. I am not huge by any means but am very body conscious, always have been I think it comes from being heavier when I was younger? When I go to the pool and see very large women in swim suits having a great time, I don't think about how big they are, but instead I am jealous that they are so confident at least on outward appearances anyways. I am very critical of myself, even if someone next to me is twice my size!
Thats how I am too, I can't stand women that pretend to give a damn when secretly they're thinking "ooh you shouldn't be wearing that love" or "ooh thank god they are bigger than me", it's such a cheap way to get a
self esteem boost, particularly when they have been fat/overweight themselves. It's not until women stop doing this to each other that some women might feel better about themselves.
As for wanting to spread the word to other fat people, I understand where that comes from (especially with young girls) but I doubt they'd appreciate it and you always run the risk of coming across someone who has a problem that Atkins or South Beach might not fix. It's a bit like an evangelical ex-smoker going on and on, these things are deeply personal from one woman to another and that kind of approach might make them feel far worse. I know that if someone ever said something like that to me, I would just question their ignorance and rudeness in approaching something so personal that any message in it would be completely lost.
I know some women do look truly awful, but hey, live and let live, they're not really hurting anyone and just because I would not choose to dress like that doesn't mean they shouldn't, too many other important things to worry about in the grand scheme of things.