The actual problem is that they've created a great surveillance tool which will inevitably get broader capabilities and they are normalising client-side data scanning (we need to eradicate terrorism, now we need to eradicate human trafficking, and now we need to eradicate tax evasion, oh, we forgot about gay russians, hmm, what about Winnie memes?).
But this was already true. There is no reason the governments couldn't have required this tool to be built at anytime all along. Remember EARN IT where Senators said figure something out (like this CSAM tool) or they'll do it for Apple? The EU is similar, with upcoming draft legislation saying they have to do it if they don't figure something (like this) out.
Back during the FBI/Apple fiasco where the government was lobbying Apple to install a backdoor to unlock phones, Apple argued that their 1st Amendment Rights were being violated, that the government could not force them to write software (since software is speech, and the government cannot force you to say something against your will)
Edit: but through regulations they could probably say 'you're not allowed to sell phones without x backdoor' but maybe the government didn't want to spell out specifically what capabilities are required.
Which is why CSAM is possibly a really interesting compromise/counter-argument. Supposedly, the only actual crime that the FBI has repeatedly sent warrants to Apple about have been child pornography/trafficking and it's an interesting stance for Apple to take here: "we'll address the actual and specific crime you seem most interested in, but will still not give you a generic backdoor".
Many of the arguments/fears about CSAM is that it can be widened to be a generic backdoor, but as you point out in the arguments Apple has already argued in court Apple doesn't seem to think a generic backdoor is a good idea and have strongly fought against it and CSAM seems to be entirely designed to not be capable as backdoor, and especially not a generic backdoor.
I absolutely understand the fears of false positives and whatever processes the FBI and other TLAs choose to do with the results from CSAM (though many of those concerns apply to everything the TLAs do regardless of what technical tools they have at their disposal), but I'm not sure that I understand all the fears that CSAM is a generic backdoor (in the making) given what Apple have revealed about how it is built and what Apple's quite explicit reasons seem to be to build it to entirely avoid building a generic backdoor and that everything about it seems a "thumb your nose at the FBI by doing what they ask explicitly for but not what they really want to build" by entirely building something that can't be used as a generic backdoor and is very specifically built to only a tiny explicit use case the FBI has asked for. At least from what I've seen so far.
You still may donate to liberty and FOSS NGOs, switch to ungoogled Android and drop macOS in favour of Linux. Also you have your rights and opportunities for activism and peaceful protest. This is not illegal yet (effectively illegal in Russia/China though).
The actual problem is that they've created a great surveillance tool which will inevitably get broader capabilities and they are normalising client-side data scanning (we need to eradicate terrorism, now we need to eradicate human trafficking, and now we need to eradicate tax evasion, oh, we forgot about gay russians, hmm, what about Winnie memes?).