Last year I realized something worse. While the women dress as stereotyped available objects (nurse, catwoman, stripper outfits, little French maid, showgirls) the men have their own roles. They're pirates, soldiers, cops, horror movie murderers, Dracula, barbarian." These roles have something in common too: they're powerfully violent and often depicted assaulting women.
What's the message? Men are rapists and women are their victims. And now every year the men and women dress that way, go to parties and bars and get sloshed, and see what happens.
Anyone is free to explore sexuality and enjoy role-playing I don't like. In this case it would be less worrisome if any if these people knew what roles they were taking on and where that might go.