Using character likenesses, or even using a brand name isn't illegal...
...as long as it's used in parody.
So obviously, everyone just needs to make all their fanart really funny! (;
But on a serious note, fanart happens. Whether we restrict it from PortCon or not, there are other people and places that are going to sell it.
I know that the AA this year was paying attention to fanart, by making sure everyone in the alley wasn't all fanartsy-fartsy but that at least half of their work was original. Of course, we don't live in a perfect world and some exceptions were made.
But fanart sells! As an artist I will say that I see nothing wrong with fanart. I DO see a problem with PLAGIARISM. I would super butt-punch anyone I met that I saw try to steal something and call it their own. The thing about fanart is, I think it's one of the best ways to get someone to notice you.
If you are an artist and I am a customer and I LOVE the way you draw, say, Yotsuba&!, I can assume I would like other things that you draw. Being able to recognize something I know I already like is what's going to pull me in. One, because we probably have at least one similar interest and two, because you did a good enough job to make the character immediately recognizable. That implies that you could draw anything, say if I want a commission of a different character/person/thing, just as well.
It would be really cool if people could only use fanart that way - gain interest and trust(trust in your talent) in your customers, and then only sell your original work; never actually sell the fanart (unless it's a commission?) I know that wouldn't be realistic immediately, but it'd be a neat idea.
I for one actually draw heaps of fanart and enjoy it more than drawing anything else, but then again, I don't sell much of anything I draw. d: