Well, that's true, but I also think it's unreasonable to expect people to think about what event they're going and dress appropriately. In the same way you might decide not to wear your super hilarious, "I'm not as think as you drunk I am," t-shirt while visiting your friend in rehab, I think it's not unreasonable to think about whether children will be present before you wear a very sexual outfit from a very sexual anime.

There are certainly shades of this, and it's not universal. If you're complaining that someone's Wonder Woman cosplay is too revealing, then comicon probably isn't for you. To me though, this is a lot more revealing and sexual than I would expect to see at comicon (and that I have seen when I've gone IRL).