I wont even attempt to define "porn".
If I had things my way, no piece of information would be illegal. Child porn, nuclear weapon plans, whatever, I don’t care, it should all be legal.
But I accept that it’s a fringe position, though a completely tenable and consistent one. It’s all information and I think it’s ridiculous to try and censor something that only exists in the abstract.
Moreover, once you start censoring you will never be able to stop. Even though I’m sure people will do bad things with information, I believe that history has shown that the good will outweigh the bad.
And, as history shows, censorship waxes and wanes in every society; you certainly can stop censoring things that once were censored.
I don't think everyone having access to nuclear plans and biological weapons is tenable. Those things aren't abstract.
Moreover, once you start censoring you will never be able to stop.
Your position become less credible. You need to argue that the censoring that is currently being proposed or being done is indeed bad for society. Or that we’d be better off without said censoring. Engaging in slippery slope style reasoning is not helpful.
Acceptance of child porn isn't tenable, that literally creates a market for rape. Sure, you may be believe markets are an unstoppable force in human nature and that suffering is inevitable, but those are just the axiomatic beliefs you've chosen to subscribe to. If you don't care about the imposition of suffering on others that these entail, are you willing to accept the same degree of insecurity for your own person?