I keep thinking about Darwin's explanation for why it's ok to check out women:...she's probably making some sort of attempt to be ornamental -- at which point a strictly aesthetic appreciation is not necessarily out of order....It sounds like a fancy way of saying she's asking for it. When you say it like that it brings up all sorts of nasty connotations.
I can't quit thinking about it because I think he's right, she is asking for it.
But I also think he's wrong. If she is dressing provocatively on purpose, that doesn't necessarily make it ok. Do two wrongs (if appreciating--ogling?--is a wrong) make a right?
Now, I hope Entropy won't think me rude to quote a post to which she's given the tag "more questions" but also "embarrassing myself", but this gives me a chance to talk about something which I think often underlies Catholic (and more generally Christian) discussions of modesty.
The starting question, I think, is what one means by "appreciating" or "ogling". I would tend to classify those two words as meaning rather different things: gentlemen may do the former, but only fellows like our lupine friend to the left do the latter.
Conflating the two is, I think, the source of a lot of talking at cross purposes in discussions about chastity and modesty, because I would maintain there is a moral difference between the two. I would think of ogling as being "looking lustfully" at a woman -- an act which is essentially one of trying to take from her, though without her knowledge. I am reminded of the one Beavis and Butthead cartoon I ever saw (someone in college thought I needed cultural broadening) in which the two anti-heroes get themselves beat up as a result of their herculean efforts to get a peek down the blouse of a busty hair stylist. It's a good example because an ogler who is trying to see a few extra square inches of breast by looking down a woman's shirt as she leans forward is trying to take something which is not offered -- and in a subtler sense, the man who is staring at a woman because he's mentally undressing her or because he finds staring at her actively arousing is deriving something from her which she is not (one hopes) trying to give. Even if she is trying to give such an effect (say, if she is the sort of young woman whose profession involves swinging about on a metal pole) a relationship between virtual strangers is not one which ought to involve providing arousal as one of its exchanges.
Now, where I think the more enthusiastic modesty advocates go off the track is in assuming that ogling (as defined above) is the only way in which a man can admire a beautiful woman. We have little doubt that people (male and female) can admire a work of art or a scenic vista without lusting to possess it. I don't think it's much of a stretch to say that one can do the same with an attractive person as well. A gentleman who admires a passing lady is not seeking to take anything from her with his gaze, or glimpse anything he's not meant to, but rather appreciating her for what she is.
Of course the difficulty is, the ogler and the admirer are physically doing my the same thing, looking at a woman who passes by, although mentally and morally they're behaving rather differently. This is, I would say, where the gentlemanly rule that you may look, but you many not be seen to be looking, comes from. If a woman sees you blatantly staring at her (and the more so if your eyes are focused too low to meet her gaze) she is likely to assume the worst, and since ogling is essentially a means of taking an unwanted intimacy with someone, she will naturally feel uncomfortable.
So I'm not here to defend any slack-jawed stare-ers, but at the same time I'd say that a man who doesn't find his attention focused on a beautiful woman as she crosses his field of vision is not so very much of a man -- and one who does is not necessarily a cad. So I would say that yes, when we dress attractively, we do "ask for" attention -- though so long one is "looking one's best" rather than "dressing provocatively" I don't see that as a problem. Indeed, there's a socially self-giving element of "looking one's best" for others, just as there's something mildly insulting to society when one purposefully looks slovenly. For instance, when a middle-aged man jiggles into a shop in a sea-side town wearing shorts, ancient deck shoes, and no shirt -- he's essentially telling everyone present: "Sure, this may be the worst sight you've seen all day, but I can't be troubled to put on decent clothes for the likes of you."
While I think it's important to observe the line which divides "attractive" from "seductive" or "provocative", I do at least want to stand up for the social virtue of being attractive to one another -- and for the gentlemen who notice, though hopefully unobtrusively, when that virtue is acted on.