Jenn, it is not my intention to shame anyone because they don't possess physical beauty. I certainly don't go up to anyone and say, "You are disgusting!" Its just that . . . you said it . . . we are mostly men here, and men are very visual creatures who (most of us) prize physical beauty. While there are exceptions, I think most men wouldn't want to walk around nude if they think their body is unattractive (frankly, a lot of us manage "ugly" fully clothed!). Most men don't understand why other people who don't look good naked would want to expose that truth.
So, maybe part of this (Nat and some others notwithstanding) is the difference between men and women. Women tend to want to protect others' feelings; men are more likely to deliver the blunt truth. So, if the average guy sees what he thinks is a truly ugly person who is naked, they are apt to overtly cringe and maybe even say, "Hey, go put some clothes on!" Women obviously understand this, as a lot of women don't even like working out in a spa around men, as they assume the men will be looking at them and thinking, "Lose the thunder thighs, lady!" Women, on the other hand, tend to take care of other people's emotions. So, while they might think that another woman is fat, unless that woman acts like a bitch, women will tend to be kind.
Which is not to say that women are never honest. It is just a matter of setting. I work in a female-dominated helping profession and have often heard what women think of other women, and of men. I've heard the date-post-mortems, in which the women trash the latest guy they went out with. I think a lot of men realize that when a woman is happy with a man, he is "Big John Holmes" . . but when she is pissed off at him and kicks him to the curb, that same guy becomes "Peewee" Herman. I know a lot of men who have gotten burned by women, and they will still acknowledge that she is good-looking, good in bed, etc. Maybe its just our way of feeling that we got something good out of it, regardless what a witch she turned out to be.
A little bit off the topic here, but I just wanted to lay out the line of thinking.
P.S. I think I can speak for most men when I say that a woman doesn't have to be model thin or gorgeous to be attractive. Some of us actually prefer a little meat on the bones.