Initially you state that people are defrauded - indeed they are, very effectively and commonly, via phone calls. Ofcom has regulated the telephone system since their inception, and can charitably be said to have achieved zero percent operational effectiveness in that time.
The Act unquestionably causes harm - it makes it effectively impossible for open, anonymous APIs because of the age verification requirements. It requires the vast majority of operators (because the UK's definition of pornography is so impossibly wide it will catch almost anything) to collect a huge tranch of information for age verification, which will cost an astonishing amount of money and prevent many community initiatives from ever getting off the ground. It will lead to many sites simply blocking adult communities entirely for economic reasons, a part of society that is already subject to substantial discrimination from UK authorities.
The Act does not include meaningful provisions for free speech. The Ofcom guidance simply says that people should be mindful of it, with no enforcement whatsoever. It is still the case that, given the penalties for not taking down illegal speech, platforms are much safer taking down much more speech than previously. Ofcom's consultation responses on their "proportionality" show they have taken a view that the actions are proportional because Ofcom say they are proportional, and no actual work has been done to demonstrate that.
You say that the UK is not a totalitarian state because it's half assed. And it's certainly true that enforcement will be capricious and arbitrary. But that is hardly a defence of the act - it will still have a remarkable chilling effect because you never know if it's you that will be targeted. Meanwhile, it will probably have very little effect on any of the things it is supposed to prohibit.
You talk in your first paragraph about how HN posters are in a bubble, but remain remarkably unaware of your own. Many communities are already discriminated against by payment providers, banks and online services, and this legislation will make those effects significantly worse, but at the same time, achieve none of it's goals.