Rahvin covered it, really.
On the other hand, my opinion on illegal merch itself has always been pretty clear: its a good option whenever theres a product you really want and cant acquire any other way, either because it doesnt officially exist (such as the license plates, or the sew-on patches someone was asking on another thread some time ago) or because I dont currently have the money or interest to hunt down the real thing. For example, before Exposures was out, there was no way to get a hold of some of those songs unless it was by paying insane amounts or tracking old versions down on Ebay etc (for which the artists themselves got no money either), so downloading them was acceptable. Its kind of the same discussion that surrounds mp3s- is it ok to download stuff, knowing the band will not get direct royalties?
The point is, there is and has never been a way to control every single profitable aspect.
On the other hand, wouldnt a DT license plate be good publicity for the band? Maybe they didnt get the $6 for the plate itself, but maybe someone got curious about the band, downloaded a song, liked them, bought the album, got their friends into the music, and so on and so on.
I always make a point in supporting the bands I admire as best as my resources allow, that is by buying their stuff and going to their concerts or reviewing their albums for our zine. People have different resources. *shrugs*