Oh, I'm more than happy to concede that point now that we have cleared it up. The problem is that the skirt/pants idea doesn't make for much of an interesting discussion.
I think this comes down to two problems with your wording (and having English as my second language, I had to rely on taking your words by their default meaning): One, the use of dress vs. skirt that we have cleared up and Two, the difference between "message about sexual availability" and "have their sexuality judged".
That's why I initially thought you were making a joke (I found it quite funny, actually) - the difference between those two is simply too great to be making a point. Women in a skirt are judged for whether or not that dresses them to be attractive. Men in a skirt are judged for whether or not they are men at all. A man wearing pants may be judged for how attractive the specific pair of pants makes him, but a woman in pants is judged for that AND for how much it makes her appear to try to be "more manly".
To sum this up - I think you were wrong implying that women are not being judged, sexually, in pants. Furthermore, the man in a skirt point doesn't hold that much value and has only little to do with that and with what you were originally commenting on - the external judgment of sexual availability.
P.S.: As for the absurdity of a cleavage being essential for a dress - it may be debatable to what extend that point really carries, but it is a fact that a dress (again, very specific, check the wiki) is specifically cut to the female anatomy, allowing for unique features of a woman (narrower hips, cleavage). The same is simply not true for a pair of pants.
I think this comes down to two problems with your wording (and having English as my second language, I had to rely on taking your words by their default meaning): One, the use of dress vs. skirt that we have cleared up and Two, the difference between "message about sexual availability" and "have their sexuality judged".
That's why I initially thought you were making a joke (I found it quite funny, actually) - the difference between those two is simply too great to be making a point. Women in a skirt are judged for whether or not that dresses them to be attractive. Men in a skirt are judged for whether or not they are men at all. A man wearing pants may be judged for how attractive the specific pair of pants makes him, but a woman in pants is judged for that AND for how much it makes her appear to try to be "more manly".
To sum this up - I think you were wrong implying that women are not being judged, sexually, in pants. Furthermore, the man in a skirt point doesn't hold that much value and has only little to do with that and with what you were originally commenting on - the external judgment of sexual availability.
P.S.: As for the absurdity of a cleavage being essential for a dress - it may be debatable to what extend that point really carries, but it is a fact that a dress (again, very specific, check the wiki) is specifically cut to the female anatomy, allowing for unique features of a woman (narrower hips, cleavage). The same is simply not true for a pair of pants.