The issue with "porn addiction" rhetoric, aside from it being scientifically unfounded, is that it's just another line that makes excuses for men.
Blaming the objectification and degradation of women and girls on "porn addicts" creates a divide -- between good men, upright men, men we love, men who would never dream of mistreating women; and bad men, predatory men, men who are evil because something within their brains is broken. It says that no, the issue isn't societal, it's an issue innate to a specific type of person. My favorite man would never do such a thing!
And this is exactly why it's so popular with conservatives, why its main proponents are religious organizations. On one hand, it takes one of the core harms done by misogyny and repackages it into something that can instead be blamed on individual moral failing. On the other, it provides a justification to attack any expression of sexuality beyond the monogamous, Christian standard by claiming that any and all sexual desire is proof of "degeneracy".