1. Some people think free speech is a pretty good idea. And it doesn't really mean much if you only defend speech that you agree with.
2. There's pretty widespread agreement that drug crimes are inhumane and should be replaced with treatment. So-called "victimless crimes". IMO, AI CP has the exact same characteristics, but it's even less damaging to society - there's no chance that someone will get into a car crash because they're "using".
3. Convictions here absolutely destroy lives. The consequence of being convicted for possession of CP is not just jail (where people absolutely do get attacked by other inmates, often times fatally), but also registry on the sexual offender list.
Do people who indirectly hurt children deserve this fate - I guess, it's complicated. It does seem out of proportion to the punishments handed out to people who kill others with cars, for example. But I can certainly get on board with some sort of criminal consequences.
But if the "offender" doesn't hurt anyone, even indirectly, that does seem like an absolute nuclear warhead of a punishment for something that most people would struggle to explain why it's a crime at all other than "it's gross".