Okay, I see what you mean, (especially with people adding extra genres just to get more attention,) but it still seems restricting. The idea feels wrong.
What if comics had to chose a single genre to be categorized as (like you said), but could have a couple of optional, secondary genres-- ones that don't affect how the series is sorted or listed, but would show up when you look at it's profile information, or something like that.
For example, maybe a comic is defined as fantasy, so it's listed with the other fantasy comics. But when you click on it, or hover over it or whatever, it'd show that it's sub-genres are comedy and romance, showing at a glance how it's different than the one that has adventure as a sub-genre.
So the secondary genres wouldn't actually do anything, but it'd help people know the general kind of comic it is before reading it. More over, it'd help the comic feel less restricted, even while the main genre made the listing of comics more orderly.
I apologize for the rudeness of my earlier remark. I am very grateful to have a service like Tapastic!
But I don't like the idea of stories being pressed into limiting restrictions, no matter how logical. Art and story telling is complex and vastly varied, and I for one (and others seem to agree) would feel restricted if I had to chose just one genre. There should be more options, not fewer. Even if those options are more streamlined and organized.
I hope I'm being clear, because I think this idea (or something like it) would help solve the problems you've mentioned, without creating the one that these people worry about.
I'm sure you guys will figure something out to solve the issues in the best way possible. Good luck!