There's a strong movement against the idea that you have to be thin to be attractive, and it's taken hold enough that there are overweight female celebrities (in non-sidekick/comedy roles), and most people on the street will agree that the hollywood ideal is too extreme.
I've seen no such movement against the idea that you have to be sexy to be attractive. If you suggest the idea (that you *don't* have to be sexy to be attractive), most people will say "yes, of course" - but have you seen any *hint* of this in practice?
Our society is extremely sexualized. Clothing is designed to draw attention to primary and secondary sexual characteristics, makeup is styled to emulate a person flushed from orgasm, everything is advertised with the implication of "you'll get sex if you buy this". In and of itself, this is not necessarily bad....
However - add onto that the moral legacy of the victorian era. Sex is bad, sex is only done with your spouse and even then you're not supposed to enjoy it, sex is not something you talk about, etc. etc. etc. We have not gotten over that, not by a long shot. (If you think you have, think again - I still catch myself working from that mindset at times, and I've spent most of the past ten years trying to break it.)
You put these two factors together - everything is about sex plus sex is bad - and you get one huge friggin' contradiction. To be attractive *and* moral, you must look, and to some extent act, like one type of person, but not actually *be* that person. (I think that element of dishonesty that seems to be culturally expected of women, and is being encouraged throughout the media, is what wyndam has been so upset about.)
And everyone is going to deal with this contradiction differently. Just as cultural standards differ about what amount of flesh is decent to expose, so are individual standards for what is just being friendly and what is leading someone on. Hell, make that individual standards of the moment - depending on a person's mood and environmental factors, they may be using different standards from moment to moment and not even realize it. Mistakes are going to happen, and when it's about as touchy an issue as sex, assumptions are going to happen that will compound the mistakes into huge raging hairballs of melodrama.
Solution? I have no solution. The world is fucked up. Sex is good, mmm'kay? But it confuses people, so be nice.
I will now go immerse myself in trigonometry.