Your entire line of thinking hinges on the premise that the politicos (and presumably, whichever oligopolies their do the biddings of) will have their way one way or the other. What you're saying is, if we don't make concessions on the client-side scanning and accept some implementation of it, the privacy-respecting tools we have now will be banned.

My question is this: why is any of this inevitable?

None of what's being proposed here solves any problem. Pedo material can be fought with the legal and technical tools we have now, as demonstrated by the news of entire pedo rings being dismantled, and pedophiles going to jail as a result on a regular basis.

The fact that you're willing to make compromises on solutions to a fake problem means that you've already acknowledged we've already lost.

The truth is, if people today were as outraged as people of my generation are over this, this false choice wouldn't have to be made at all. Things are just fine the way they are today, and you don't have to give up anything if you don't assume you'll have to give something up.