As a company promoting new products/software/games and whatever, it would be a pain to have fans shout and rage in the middle of their conference. Which i know for a fact would happen.
But kicking out people JUST for cosplaying as a MM character or wearing a MM related item is incomprehensibly ignorant. As much as Capcom deserves being yelled at though, they're still a company, thus at a higher authority than the "normal" people there. They get enough rants over the web anyway.
The reasonable thing to do would be to escort people out if they get out of hand, but not kick them out just for showing support for something they idolize.