Earlier quoted context omitted.
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…
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.