So, is cosplay killing comic cons?
No. And suggesting otherwise is, frankly, pretty stupid.
Don't get me wrong, I feel bad if talented veteran creators are losing money when appearing at cons. But blaming the enthusiasm of fans - any fans - is shortsighted, misguided, and just plain rude.
You want to get fans' money? Then maybe you don't attack, blame, accuse, or otherwise malign those fans.
As cons and the geeky culture they celebrate have grown in popularity, they have also grown in size, scope, and number. There are more shows with more things competing for fans' attention and money. Fans' bank accounts haven't grown in proportion with the shows themselves, however, so something has to give somewhere. It's too bad that anyone has to suffer as a result, but that's how it goes sometimes.
Blaming any one enthusiastic subset of people is just trying to find a convenient scapegoat to hang larger problems upon. And by the way, cosplay has always been a part of convention culture, so it's not like this is a new fad or anything; if more people are doing it now than before, it's because they've realized it's like getting bonus Halloweens, who can blame them for wanting to jump on that?
Cons have always been as much about the social aspects as about the retail ones, and now that you can buy comics and toys and whatever else very easily in person and online, socializing plays a bigger part than ever. They're a chance to get together with likeminded folks and, yes, maybe be someone else for a few hours. When you rail against that, it's hard not to come off looking like Abe Simpson.