My first post listed a whole load of problems and solutions that have been proposed. I shall try and focus on the things that I think you are concerned about, but if I am putting words in your mouth please let me know what you think are the important issues you want my opinion on.Given that there is a problem what alternatives are you proposing?
Children being harmed in the creation kiddie porn
It is a very difficult problem by its nature. If I was in charge of this, the first thing I would do would be to quantify the problem and find out where and how it is happening. A quick google gives no ideas of the incidence, and I do not want to know the details. Without that I could not realistically say what magnitude of investment should be made and where.
If I was given money and political will and told to make the biggest difference I would focus on education, particularly of peers identifying each other who are at risk, as well as making sure everyone knows who to call if they are exposed to it. The other thing that would probably make the biggest difference would be something approaching an open borders immigration policy that would allow people to escape desperate situations, but that is a whole other thing. I just cannot see a way one could make a difference to this problem by restricting encryption.
Children being harmed by accidentally coming across porn
This is one that is made out to be a problem, and if it really is but I am not convinced. They may come across the odd expose breast in an inappropriate advert, but I have not had the "window cascade" of hardcore porn that used to come up when researching certain subjects like you used to get.
If it really is a problem that needs solving then it should be solvable. A legally required click through "Are you over 18, porn ahead" before you get to porn does not seem to invasive. They had the idea of restricting porn to certain top level domains I think, like .xxx. Again, that does not sound too invasive but I am not sure it could work with the global nature of the internet.
Children being harmed by purposefully accessing porn
This is another difficult one, mostly because in many cases by the time they are interested in porn many children will be better than their parents at working computers. How do you design a childproof system when the children are better than the parents are using the system?
I have said before that on a practical level I think the only answer that would allow most parents to control their children's internet usage without causing more harm than good is to require the children to use a desktop in the common area of the house until they are old enough to be trusted to control their use. I think last time we talked about this uppi convinced me he could lock down a system such that they would at least know if their child had unlocked it. I would put money on less than 50% of parents of teenages being able to do that.
Id for porn use will fail. No one will give their real personal id to a third party to identify themselves as a porn user. It will be so much easier to stop getting legal porn from pornhub and start getting illegal porn from [places] than go through the bureaucracy and risk. Then everyone will be exposed to illegal porn instead of legal porn and that will do harm.
Adults being harmed by purposefully accessing legal porn
Make more harmful porn illegal? I have to admit I do not know what the line between legal and illegal is, and I am not sure I want to know, but if there is good reason to believe it is in the wrong place there is nothing wrong with moving it.
Adults being harmed by purposefully accessing illegal porn
Another difficult one. More investment in enforcement (we could use the strategy we are using against the dark web against illegal porn perhaps?) More severe penalties, but is that justified? Automated searches of all MPs computers sounds like it might be a good start.