I think it's totally reasonable for women to want to look attractive, even when they dress up. Even if your outfit is truly spectacular and hilarious, you probably won't feel as awesome in it if you know you, in your totally vain way, look unattractive in it.
For me, what's bothersome, is ALL of the out of the box standard "sexy" outfits. Sexy witch, sexy cat, sexy pirate, sexy school girl, sexy nurse, whatever. I mean come on at least be creative. I had a friend go as a crossword puzzle using black tights, heels, a black top hat and a white pillowcase with the crossword on the back and the hints on the front. It ended up super sleek looking, people got the chance to touch her and stare at her while they filled out the puzzle, and it was also really creative and fun. I saw a group of girls put together a really cute version of the ninja turtles, which was also cool.
Whenever I see sexy witches, cats, nurses, whatever on halloween, I know their real intention is JUST to evoke sex, not halloween good times accomplished while being attractive. They're saying look at me, I'm a sexy cat. Not look at how baller and creative my outfit is and how kickass I look in it. I much prefer the latter.