Is there a contingent in the cosplay community that's explicitly sexual?
There's certainly a dash of it!
Cosplay can oftentimes be about self-empowerment. I mean, there are certainly some people showing off, and certainly some people who will cosplay one way or the other inappropriately with many of the wrong reasons in mind. There will also be people who are consumers in a way who really dig that.
One of my favourite cosplayers is super sexual, to the point where she starts to get edgy. That's OK! Its what she wants and more power to her.
Your initial comment made it seem like it was everywhere and too rampant. Its not dude - its just a bit of self expression. Yeah its sexy, yeah there's the possibility that its intended to be exploitative (and if it is, shame on them), but to me it just seems part and parcel of the whole Cosplay thing. Let it all out in as tasteful a manner as you can manage!
Video games, comic books (especially), regular books, movies, etc often have a strong power fantasy associated with them. Dressing up is a part of taking that power.
I've cosplayed the Ice King before, won an award for my performance as Simon Petrikov. The costume was incomplete and had as many inaccuracies as my own personal touch of details. It was about me taking that power and taking that person.
Sometimes these things are sexy instead of depressing like the Ice King! Its all about taking it and really wearing the mantle of the persona that you pick up. Looks can be part of that power. One day I want to look sculpted and built and wear something shirtless and badass. That's totally equivalent to the outfits that exhibit the female form. Some people want to be that fantasy, to wield the power of their character by taking its form.
There's some real primal, ancient stuff going on. This whole power dynamic thing has been going on for some time, and from where I stand that's really a bit part of what makes Cosplay such an art form.
Yeah there are creeps and such. I get that you see a lot of the more sexual stuff, and yeah sex sure sells. Focus on the positive stuff I've outlined here. You'll probably notice the positivity more and hey, help flush out the more derogatory stuff! It doesn't have to be derogatory.
I do find you a mighty bit off base if you think it is derogatory. Of course, I do not speak for everyone, but there you have it.