"Hey, mister sketch it man, will you draw me a Calvin peeing on Osama Bin Laden?"
"If you're such a good artist then you ought to be able to draw Homer Simpson. Draw me a Homer."
"Can you put a big swoosh on my head and a word bubble where I say, 'Just do it.'?"
While all of these are interesting artistic challenges, I can't and won't do them. Why? Because of certain non-person entities called corporations that have convinced the powers that be that it's a good idea to restrict the flow of creativity with a little thing called the Digital Millenium Copyright Act. Actually, a lot of the restrictions regarding copyright were put in place in the US Copyright Act of 1976.
Either way, as an artist, I am boxed in as to what I can draw and post online. What about "fair use?" Well, we can cross that bridge when we get to it. Those sorts of things must be decided on a case by case basis.