Do you think children are harmed by porn? Did you know it's illegal to distribute porn to a minor in the US?
It seems reasonable to me to hold porn companies responsible for distributing porn to minors.
That's a discussion that's entirely tangential to age verification. However, I think porn should be illegal entirely as it's just prostitution. As such I think porn companies should not exist, the same as brothels or heroin dealers. If they have to exist for practical reasons along with other objectively harmful things, such as alcohol, marijuana or gambling, then obviously they should be regulated to ensure they're not targeting minors.
That does not detract from the fact that the people arguing for age verification are using "think of the children" in order to push surveillance.
There is actually extremely little evidence for anything when comes to individuals, sexual content, and their sexual fantasies. There is even less evidence available for anything when it comes to minors.
I've read papers on the topic, and the good papers always point out that there is almost no focus on any potential positives. Many "authors" have already made up their minds before they've even started conducting research, and that's only if they manage to get funding (everything sex related gets very little or no research funding).