The main objections that I've read regarding this issue is that it actually has very little to do with blocking access to pornography for children. Most people are concerned that it's a way to introduce mechanisms to censor the internet or even worse to track people's personal sexual foibles as possible ammunition against dissenting voices. I have no particular interest in pornography but this really is a small step towards authoritarianism.
I agree with this.
Apart from anything else, I'm guessing that Mumsnet would find its way on to a whole load of blacklists because of the copious swearing and a lot of the 'frank' subjects discussed.
My son likes TV gameshows and related info/trivia. He looked up Stephen Mulhern's Wikipedia page after watching Celebrity Catchphrase and even that fell foul of the parental controls as 'gambling' and was blocked. What's the betting that many harmless clothes retailers selling 'nude' tights, shoes or whatever find themselves blocked by sophisticated algorithms with no human common sense.
Assuming that you want to keep using MN, you would maybe then have to pay £4.99 to prove that you're an adult.
Meanwhile, you're now on a list of people who view porn. Don't bother protesting that you only want to use MN - don't you think it's, um, 'convenient' that you can now access all adult material under the 'guise' of only wanting to use an online parenting forum?
Yes, you've made it 'clear' what kind of person you are - and now you're on that list which will doubtless before long be made available throughout all government departments, including child protection - as well as any half-decent hackers/spammers/ransom-seekers, or just people who find a 'lost' government laptop of memory stick on a bus.
I wouldn't at all put it past certain companies to deliberately set up 'gatekeeper' sites - ostensibly reasonable legitimate weighty adult-orientated sites (such as, say, politics or economics as opposed to CBeebies) - which 'unfortunately' fall foul of the censors and so require you on a technicality to register your details as an adult - which then subsequently lets you into whatever filth on other sites that you fancy.
Conversely, if the ruling is sites that host a minimum of a third porn, there will be immense amounts of boring/randomly-generated filler content produced for the sole purpose of constituting 70% of a website, albeit 70% that 'astonishingly' happens never to get any traffic.
This quite probably happens naturally anyway with many huge, comprehensive sites that are completely above board. How many people actively look for Val Doonican songs on Spotify as opposed to those wanting Taylor Swift tracks? MN itself has loads of specific categories, yet I bet that at least 70% of the traffic rarely leaves AIBU or Chat.