No, the child isn't being directly harmed by someone viewing their exploitation, however their honor and dignity are chipped away at with each viewing. Just because the video was already made -- the brunt of the damage has been done -- doesn't give us all the right to see it guilt-free. And completely decriminalizing possession would send an implicit message that the depictions themselves are acceptable.
That said, I certainly agree punishments shouldn't be anywhere near what they are today for mere possession, especially since regardless of conviction the person's life is oft-times destroyed upon mere accusation. (And as for your comparison up there, I actually think possessing videos depicting real murder should carry a similar punishment.)
Of course, as others have mentioned rational thought frequently doesn't enter the picture at all when this subject is on the table, so I see things getting worse, not better. The public hysteria has really reached a fever pitch with stuff like drawings being deemed child porn, or kids taking cell phone pics of THEMSELVES getting charged. It's classic witch hunt mentality, where you literally can't say ANYTHING against someone once they've played the pedophile card without eyes narrowing and the accusations swinging your way. "Oh, you're sticking up for the CHILD MOLESTERS, are you?! Methinks you may be one of them!" ::torches raise:: "GET HIM!"
And society's hypocrisy makes the whole thing even more ludicrous -- in the US anyway -- where the age of consent is 18 (if you're EVER attracted to anything below you're automatically pure evil -- no ifs, ands, or buts), and yet models regularly start their careers at 13/14, and marketing and media bombards us with idealized images of youth around the clock.