Copyright is never an easy issue especially when it comes to artwork that has the potential to be infinately copied. Some of us my be unconcerned if our work is downloaded and used by others but their may be contexts in which there would be objections. Far beyond the question of monetary reward or attribution as the "original" author. What if someone used your work to promote a cause to which you have a moral objection?
Creative Commons licensing is perhaps more helpful for protecting your work whilst still making it available for broader cultural sharing.
On another note relating to copyright have a look at Nina Paley's TED Talk “Copyright Is Brain Damage,” she believes copyright ultimately hurts more than it helps.
