It is insanely touchy, and granted Japan hasn't put out anything crowd-pulling in a while (Naruto, Bleach, FMA), even though it's had some small hits (ie. Death Note). But when you think about what you're going to cosplay you think about how long you're going to wear it and how comfortable it may or may not be. It's why some girls change out of their costumes, or opt for flats instead of heels. It's why some prefer to wear a costume with jeans and a T (like Homestuck), even if it means a bit of uncomfortableness (horns and the bodypaint); It's overall comfortable. And yes, Kumoricon is welcoming to it. I never saw anyone jumping into the Homestuck photoshoot thread and putting a stop to it. Likewise to the My Little Pony thread. If people are so bothered by it, they should look at their own decisions and keep in mind that fans will wear what they want.
Sure, I was put off that so many weren't in costumes I could recognize this year, but that made those that I did know all the more gems to me. And really, if you take everyone who was wearing Naruto, Bleach, MLP, FMA and Homestuck and lumped them together, they're kind of equal. It might die down in a year or two, like the others, and they'll be cosplaying something else they enjoy.
However, it will also "die" if we continue to present an attitude of being offended and unwelcoming to these fellow con-goers, no matter the reason they attend.