A little logic, as to why you cannot compare someone who views child porn to someone who smokes weed.
1) Assume that a man is sitting at home, smoking weed, and watching child porn.
2) Smoking weed, by itself, does not harm others. Others are not murdered, maimed, or caused psychological damage because of the weed itself. Yes, the cartels do kill people, but that is the cartels, not the product itself. If I wanted to grow weed myself, I would grow it, then smoke it. Nobody is hurt.
3) The harm in child porn is in the porn itself. If I wanted to make child porn to watch later, I would have to abuse a child to do it. By the very act of ordering child porn, I have automatically caused harm to a child, no matter if there is other crime surrounding it or not.
4) There is no comparison here. The violent crime that occurs incidentally in both weed and child porn are the red herrings in your argument. When you look to the actual product, one is harmless, the other harms kids. If one orders a product that automatically harms kids, then he is just as guilty as the producer of that product.
What's not to understand here?