I don't know where the "should" comes from in all this ...

"Should people pay more for what I do? A survey of myself and others like me says 'yes'!" Uh, OK :)

And BTW, if you license something with the GPL, that means that anybody can legally copy it, modify it, give it away, etc. as long as they too abide by the GPL. The GPL isn't just some magic selling point that you can attach to something, and then still complain when people use the very freedoms that the GPL explicitly provides. If you don't want to provide those freedoms, then don't license your work with the GPL.