If it's pornography of an unwilling subject, surely the distribution and consumption is harmful to the subject, as it's a violation of their privacy and integrity.
If someone had put secret cameras in your bedroom, would you be completely cool with them selling the pictures online?
What if you were abused, let's say threatened with a weapon and forced to undress in front of a camera, a traumatic experience for sure. Afterwards you learn that the film is being traded between people who get off on this stuff. Would that really not feel like a further violation?
Would you really be unaffected by the knowledge that for the rest of your life, at any time, there could be creeps getting off on your abuse?
A stronger argument IMO is that those types of crimes are premeditated, calculated and committed by those who have many other options. So deterrents are likely to actually work against them.
Not that I agree with you. But there's an argument to be made for using deterrents where they are likely to work. Rather than against the desperate or impulsive.