Is it for the sake of humility? Or modesty? And if a veil causes you to stand out because no other woman is wearing one, should you refrain? Some dismiss the argument that women should not dress out of respect for the weakness of men because it is a problem for men not women, and they may even try to use a reductio argument targeting with a slippery slope objection -- how much modesty is enough, if a man can be stimulated even by ----.
I think the argument could be made that St. Paul was not giving a precept for a specific culture or in reaction to something (only prostitutes were unveiled, etc.). If it is the case that hair is a marker for health and vitality and a sign that a woman is a suitable mate, something that men instinctively look at when judging whether to pair with a woman or not, I don't now if I would call this a weakness or attribute this to original sin. I think a man may be attracted or look at a woman without any sexual concupiscence, though it could be said that being moved by nature, without will, to look at an attractive female may be a part of general concupiscence. Weakness in the sense that it is not wholly voluntary, then, taking notice of an attractive women.*
It may be easier for a man to stop looking if he can't see the hair (just as if a woman is wearing modest clothing). Uncovered hair, on the other hand, is something that men will "naturally" look at, not because of some sexual fetish but because it is an indicator of health. While a chapel veil may be an oddity at an OF liturgy, I think most men will get used to it after a while, and they won't stare at a veil just because it is there -- it doesn't have the same sort of significance as hair. (Though it may signal that the woman wearing it has traditionalist tendencies and may be the sort of woman he would want to marry... and then she'll be a source of distraction of him as a result.)
Yes, the face can also be diverting, but if a man is standing behind a woman, he won't be looking at her face, but he may be looking at her hair. Similarly, for a woman
I suppose the ancient Christians had reasons for separating the sexes -- some even drew up a curtain between the two groups.
What about the (over-)use of cosmetics by women going to church? Are they drawing too much attention to themselves, even if they are doing so mostly out of habit and unthinkingly? What about dressing up for church, as opposed to dressing "modestly"?
When did the wearing of hats become the dominant practice in the UK? I think many of the hats worn at the Royal Wedding last week were counter to modesty--another occasion for women trying to make a fashion statement or draw attention to themselves.
Anyways, I wasn't trying to give a final answer on the question on whether the precept to wear a veil in church was applicable to all human societies, but what people have written about hair as a signal to physical/sexual attraction got me thinking about the precept in relation to that.
Something from Ed Peters.
Edit. Alte has something on the topic.
*Postscript. After more consideration --
The looking at hair seems to be instinctual for men. That observation of hair (or the face, etc.) can lead a man to gaze upon a woman because of an attractiveness, or desire to do so though he should be occupied with other matters, is due to concupiscence. The difficulty in understanding this may be due to an erroneous association of concupiscence with only the sexual appetite.