It would be so easy, technologically, to require porn all be on a domain ending in .xxx, then just filter by that. But it will never happen.
Yes, there would be discussions about what is porn, but that wouldn't change from where we're at today. It's just the technology would be so much easier to handle. Instead, I have to block google.com, because it's way too easy to get porn just by access to that. I have to block emoji (and gif) searches, because you can get porn that way. I have to block access to things my kid's schools say they need access to for homework. It's dumb and exhausting trying to keep up with it all.