Definitely child porn should be illegal. I believe studies have shown that porn does incite violators to act on their fantasies. The sexual predator is an entirely separate class of psychological stew anyway, and pedophiles are definitely sexual predators. I believe that those looking are also most likely doing or will attempt to do so. Plus, just like a couple might watch porn for "ideas", so do predators. It's a training class.
Child sexual abuse is probably as old as mankind, and yet is more violent and rampant now. Blame this on whatever you will, but I believe making kiddie porn illegal is, if nothing else, a statement that as a society, we will not tolerate pedophilia.
There is an audience for dang near anything and just like a heroin dealer, there's always someone there to prey on the weakness of others. I think there is a connection between condoning or accepting deviant behaviors and the numbers who practice said behaviors. Not absolutely, but peer pressure and groupthink are powerful things.