", and by possessing it you are creating a market for it which harms more children daily."

No, this is nonsense. Mere possessing of information is not creating any market, regardless how sickening the stuff is. Only purchasing is harmful. Vitalik is very logical. The point is that CP is no material but information which can be inflated (copied) infinitely which would rather destroy the market. Or are you suggesting that police authorities are helping to create a market for CP by saving and analyzing such material? Or How about journalists? We are not talking about distribution, which is yet something different.
Prohibition of possession can actually boost the market and hamper the fight against CP production, where the real crime happens. CP can also be used to hack and smear some computer of an innocent and also for blackmail if possession is illegal, which poses an immense power for rough actors. I have no final opinion and I see the problem, but things are not that simple. There were cases where innocent tourists not knowing they carry drugs in their luggage where sentenced to death in some asian countries.
Your and many other comments are hysterical and promote dangerous witch hunt and thought policing.
Vitalik chose CP as the most extreme example to express his point. His only mistake was to expect other people to be as cool minded and logical as he is himself.