I'm not sure what you mean by "fair." There are plenty of things that go on, at cons and elsewhere, that I don't necessarily want to see, and I'm not talking about anything touchy or remotely sexual at all. There are programs, classes, vendors, etc. that I don't want to do or see, but would it be fair of me to ask that everything I don't want be removed from the venue? There are even people with too many piercings or wearing odd clothes or the wrong kinds of tattoos or political bumper stickers that I might not agree with, but do I have the right to ask them to leave? Is that fair? Similarly, if people don't want to see breasts being touched, they don't have to look or participate.

And as for being given the option to consent...they did have it, once they arrived at the con. Seeing so many similar buttons around it would be an easy manner to ask someone wearing one, what they represented, and then make their choice.