It's not a strong point because you can make exactly the same argument for anything else you'd like to ban, including printable pistol schematics, anarchist cookbooks, terrorist propaganda, and so on. It's a cheap truism to say that if something is easily available this will make it more likely for people to become interested in it, will make certain people more inclined towards it, may create a market for it, and so on, than if the same thing was hard to find or not available at all. Yes, probably it will.

Who gets hurt in the process of making pistol schematics? Or in the making of terrorist propaganda?

The hard difference is: With CP, harm is done in the process of creating the material. With most other things, harm could potentially be done as a result of the content.

That wasn't your argument, though. There is no doubt that the production of CP is and should be illegal, as it involves child abuse. However, your original argument was about the possession of CP. There is a standard argument against the claim that this is a victimless crime, and that is that the children abused are harmed by the distribution of pictures that show them. I find that argument to some extent convincing, but not yours.

That is quite literally what I said though.

No, you suggested that the harm caused in the production is a reason for criminalizing possession, which is what I disagree with. I accept other reasons in this case, but not this one. Which of these positions you endorse has far-reaching consequences for the moral and legal evaluation.

It's similar with the "war on drugs" or when you want to evaluate the morality of your sneakers and clothes. Should possession of the drugs be illegal because people were harmed in their production (by e.g. drug cartels), should possession of the clothes be illegal because they were produced with child labour? I don't think so.

Edit: To make this clear, I merely replied again to clarify the difference not because I think there is a huge disagreement. This is obviously an unpleasant and contentious topic and I very much hope I don't come across as a CP apologist - I'm not, for the other reason I've mentioned.

Where did I ever imply anything should be criminalized or not?

My point is: There's a clear distinction between material that inherently causes harm in its creation and content that may lead to harm in some way.

Your extension to drugs or clothing only partially makes sense, as those can be produced without causing harm to or exploiting anybody. I view it as more similar to (knowingly) buying stolen goods.

I see your point now. That makes sense to me. Thanks for taking the patience to explain your view in detail!