There's also the argument that CSAM can act as a gateway leading people from just being a pedophile in their head, to going out and doing something to some child.
Yes, it’s an argument but there’s zero data to support it, in fact the opposite.
If this were true then widespread availability of pornography on the internet would have resulted in a massive increase in rape of adult females. When in fact, assault numbers have been on a steady decline for decades.
Yes, this is an argument that exists. But it's not supported by evidence. It's the same as the old "video game violence should be outlawed because it might cause real violence", which is just as unsubstantiated.