Research indicates younger ids who stumble across porn accidentally can find it shocking and disturbing although the majority of young people surveyed in a 2020 British Board of Film Classification (BBFC) report said this didn't impact them in the long term.
Nobody is visiting porn sites accidentally anymore. This ain't the 90s. They don't pop up in any mainstream search engines by default.
Unless this includes not only porn sites but any site that might potentially host porn (like Reddit, Twitter, Facebook, or really any site with user-uploaded content), this argument is invalid (as well as specious).