First off, I'm going to give my understanding of what beautiful means in this context: Not necessarily attractive, but possessing physical elements pleasing to the eye. This encompasses but men and women.
I understand that you think women are naturally beautiful, and I respect that, and I more or less agree. My problem is that you appear to be objectifying. It is an extremely old-fashioned view that women should strive to be beautiful. I mean, think about the problem of self-esteem issues among young women today. Media is only intensifying girls' desire for beauty, and for those who feel they haven't achieved that, there can be serious implications, into which I won't go right now. Also there's the whole subject of bullying if a girl doesn't conform to society's view of beauty. You mentioned that society's influence was the reason for women wanting to, as you might put it, intentionally make themselves ugly. Get real.
Anyway, why should women strive to look beautiful? If they are naturally beautiful then how would dressing in a masculine manner make any difference? Personally, I have short hair, I wear men's clothes, I don't wear make-up, and yet I can still look in the mirror in the morning and go, "Damn, I look really pretty today." Personal style has nothing to do with beauty. Think of it this way- A girl with perfectly styled hair and perfectly applied make-up wears a body-hugging dress to show off her figure. The next day she wears baggy, every-day clothes, doesn't do her hair and make-up. She feels like being a bit boyish. Does that make her ugly? She's still the same girl underneath her two styles. And the absolute same applies to males. And what about transgender FtM? Those boys don't want people looking at them and saying that they should be more feminine, in the way that trans MtF don't want people saying they should stop being so girly. It's the nature of some people, and if you can't agree with that, then you need to find a cave to live in.
And I haven't even started on the actually subject of crossplay. I crossplay. Actually I rarely do a female cosplay at all. Know why? Because I like the male characters. I also like to show respect for the creators by depicting the characters in the way they're supposed to look. I'm not about to sacrifice accuracy for the sake of femininity. There are more important things in cosplay than keeping to your own gender. Everyone agrees that cosplaying is an art form, and well, crossplaying is an extension of that. I put effort into my work. I try my hardest to look like the male characters I cosplay, and even if I don't completely pull it off, I feel as though I've done the character some level of justice by not changing them to suit me. Also, I can look in the mirror and say, "I look really good like this." I see beauty in my male appearance as well as my natural female. I can appreciate both. I've seen FtM crossplayers and thought "Wow she makes one fine man." I've also thought the very same of MtF crossplayers at times. Both genders have an element of beauty in them. So who really cares if a girl cosplays a boy? Who cares if a boy cosplays a girl? They'll still be beautiful human beings.
Please get your head out of the clouds. We're not in the 19th Century anymore.
Rant over. Phew.
Planned cosplays for the next few.... years?
1. John Watson- BBC Sherlock
2. Loki- Thor, Tales of Asgard
3. Frodo Baggins- The Lord of the Rings
4. Bilbo Baggins- The Hobbit
5. Thranduil (Randy Thrandy)- The Hobbit