> I mostly disagree with it. I don't want prepubescent children watching porn of course, but the vast majority of them aren't doing that with any regularity,

This genuinely needs qualification and I suspect, based on discussions I have had with friends who are teachers and teaching assistants, that you would be horrified by how often very young children (seven, eight, nine years old) are viewing material that only a couple of generations ago would not have been seen in any legal publication in the UK.

> It isn't a problem that demands a robust solution with serious downsides.

This is an opinion, not a fact. I think I disagree, but I also disagree that websites asking you to verify you can access a particular link on a mobile device is a particularly serious downside (since that is one of the valid ways of age attestation in the UK -- it requires only that your mobile phone provider knows you are an adult, which they can establish in a number of ways).