You've gone pretty extreme there. There is a much more plausible explanation, which is that they genuinely believe that more people would be saved if the security services could access messaging apps and they don't think the level of potential abuse is worth worrying about.
Don't get me wrong, I think they have made bad decisions etc. but in this case, I think it is simply naive "if you haven't done anything wrong..."
I think both can be true: the government believes it can increase security in general by expanding the state's surveillance powers--the state always wants to trade privacy for security. However, they're not framing it as a general "give us more surveillance powers and we'll increase security"; they're framing it narrowly as about protecting children ("give us more surveillance powers and we promise we'll only use them to protect sexually exploited children") which is exploiting victimized children in my book.
I do think that it's naive to think that one of the most important countries in the world with a rather effective intelligence service and a lot of smart people everywhere in the state is naive. I really don't think the UK government believes that if they remove encryption from popular chat apps the tiny percentage of population that might use it for evil purposes will be caught instead of, you know, moving to a different mechanism.
There's an even more plausible explanation, which is that both are true. They're aware that stopping encryption might save a few children, but they're also aware that it enables the mechanisms of the surveillance state that give them extraordinary power over the public. They want to stop child sex trafficking and they want to abuse people's privacy.
I've also heard Conservative MPs say that "lockdown measures were against our freedom-loving sensitivities" or something similar, so they at least acknowledge the value of freedom to the population.
Our ruling class cannot plead ignorance as an excuse.
I think the more-plausible thing is that this part of that Red Meat programme, which is going to consist of a train of announcements designed to appeal to rightwing Conservatives, none of which will have anything at all to do with the Prime Minister.
This Red Meat programme will also distract the opposition away from the Prime Minister's moral emptiness and deceitfulness; the government hopes that by making sufficiently-nasty policy proposals, they can force the opposition to devote their time and attention away from the weaknesses of the Prime Minister and his coterie, and towards opposing these proposals. It's very cynical.
Forecast: I have a long record of wrong political prophesies! But I think Boris will have gone within a week. I have no idea who they will replace him with; none of his colleagues has electoral appeal, as far as I can see, and they're facing a General Election in two years. I wouldn't offer odds on the outcome of that election, either; the leader of the opposition isn't particularly appealing, is not loved by his party, and seems to have no policies.
I have to admit - I was expecting Brexit, Trump, and a massive Tory majority at the last GE (not rubbing it in - good lord I wish I had been wrong about all of these), but I really don't know how much road Johnson has left to run. I really think it's getting shorter now every day. The (liberal) press have made a big deal about everything else so far, but the lockdown parties (sorry, meetings) I think are the first 'real' big hits to him that people will actually care about. It's genuinely going to get bumpy for him, but he was smart and filled his cabinet mostly with people who just aren't that clever and are dedicated to him - I don't think there's anyone who knows when to make the first move. I think he can only really be removed when there's someone ready to replace him.