I posted this on the MALE modesty thread, but think it's relevant here too --
Well, there's more to covering up than not to be a temptation. Modesty is more than just that. So, for instance, you might have a man or woman who is seriously overweight or otherwise extremely unattractive. If they were to expose themselves, they would not only NOT be a temptation, but it might actually have the OPPOSITE effect, to turn people off to allures of the flesh. So are unsightly women exempt from the rules of modesty? Of course not. Just because they do not cause temptation in men, they can run around half naked? Similarly for a man. Just because he might not pose a temptation to any woman, then it's OK for him to run around shirtless? It bothers me when I see men walking around in public without their shirts on ... and not because I'm the least bit "tempted" by them. Why then? Because for anyone, whether a temptation or not, to run around partially undressed creates and ATMOSPHERE and a CULTURE of immodesty in general. Even my younger children, when they see a man walking around in public without his shirt on, find it shocking and ask, "Why is he naked?"
There's something there about how we comport ourselves as temples of the Holy Spirit ... as St. Paul taught, with dignity and decorum. Similarly with men. So, even IF I know that I will not cause temptation to anyone, I would be embarrassed to walk around without a shirt on [and not because I'm unsightly or anything, since I work out and have a good physique]. Even among [straight] men, I would be very reluctant to take my shirt off. When I was a kid, even before the notion of being attracted to women presented itself to my mind, I was embarrassed to be "skins" when we played shirts-and-skins. When I was at High School and we had to shower with other boys in an open shower at the gym, that embarrassed me. When I was a very young boy, maybe 4 or 5, for some reason my Mom took a picture of me when I was taking a bath, and I immediately placed my hands over my private parts. So, even apart from the problem of causing someone else a temptation, there's a natural instinct we have towards modesty.
When we cover up, we are presenting ourselves as human beings, as people with souls created in the image and likeness of God, with higher faculties, intellect and will. When we run around half naked, we are presenting ourselves (and relating to other people) as mere bodies and flesh. But we are temples of the Holy Spirit, and being properly attired helps to present itself that way to others. And the same thing goes for dressing like slobs. Most people run around in public dressed like slobs even when they're not being immodest. People used to dress with much more dignity and decorum in earlier societies that were more civilized. Then women might wear tons of makeup and lots of Jєωelry. Even if done in such a way as not to actually cause a temptation, they still present themselves as extremely focused on themselves as mere flesh, as animals, rather than as souls created in the image and likeness of God. Or when certain cultures of men wear tons of "bling".
More and more these days, you'll see men running around in public without their shirts on. And the other question, then, is WHY they are doing it. At the gym, there are some guys who wear next to nothing on their upper bodies, and are well built ... and I often notice them in front of the mirror flexing and checking themselves out. Many of these run around like that because they're trying to get attention from women. [Croix, is that you?] Even if the women aren't tempted per se, they're hoping to get a look, to have some woman "check" them out. So a lot of the motivation behind guys taking their shirts off is impure in the sense of their wanting to be noticed for their physique ... so an impure vanity. Not to mention that vanity in a man is even uglier than in a woman, because there's something more natural (albeit in a Fallen Nature type of way) for a woman to want to be attractive than for a man. Frankly, these guys strike me as borderline gαy ... so obsessed are they with vanity. So, because men don't pose as strong a temptation to women as the other way around, it's OK for a man strutting his half-naked stuff around trying to get women to look at him and check him out? Even if he doesn't actually provoke a sin right there on the spot, he's getting the INTEREST of women, who might become more and more interested in the physical attractiveness of men. So even while not directly sin, it may be creating habits and inclinations and patterns of thinking that might ULTIMATELY lead to sin. Not to mention the bad example they are setting, and even potentially resentment from women. From time to time one reads of women who expose themselves in public in order to protest the double standard. Hey, if men can walk around without their shirts, why can't we? That's sexist, they claim.
Would I want my teenage daughter mixing with a group of boys without their shirts on? Certainly not. Even if it doesn't cause her to commit an immediate sin, it can still cause an at-least-vague sense of attraction and physical interest in the opposite sex ... that probably would not lead anywhere good in the end.
As for art, very few men are tempted by PAINTINGS of nude women, far fewer, at any rate, than would be tempted by the sight of an actual nude woman. Similarly, if a woman were to see a very well built man without a shirt, that would undoubtedly be more of a temptation than a painting.
So, in short, to view modesty merely with regard to its potential to cause an immediate sinful reaction is WAY too narrow a perspective on the subject. St. Paul doesn't write about it that way at all.