If you Cosplay, then you are part of a grass roots marketing campaign for that character. Make no mistake about it, if you take someone else's character, make a costume that character wears, walk around in public and at Cons dressed in it, posing in it, letting people take pictures of you wearing it, then you are advertising that character. If the owners of the character do not pay you to do this and you have paid to make the costume, paid for room & board at the Con and paid entrance fees to contests, then you have paid money out of your own pocket to advertise someone else's property. If you can accept this as your choice, then good for you, but do not for one second believe that you have performed an act of creation. You may have crafted a translation of the character, but there was no creation involved.