Yep. Argument one is, this system will quickly be used mostly for other things.
Argument two: Even if you can stop 100% the transmission of CSAM materials, you are not stopping the abuse of children. Just the secondary abuse of distributing the materials.
It happened almost immediately in Australia with COVID tracking data[1].
Were I in a position of any type of authority, careers would be ending and jail time would be getting handed out like candy over this. I'm not in charge unfortunately and not enough citizens know how to react to these expansions of power until it impacts them personally.
But as soon as the capability exists, it really is a slippery slope: it's far easier to gradually expand the scope and reach by administrative changes, then it is to start the program up initially - and there's no track record of any government reasonably resisting this sort of insider threat.
Exactly right - and initially the expanded use of these systems is not visible. PRISM, for example, was found to be used frequently by NSA employees to look into the activities of romantic interests or exes. Nobody knew about it for years until an audit took place. We're told that the abuse of this system was unusual and handled appropriately, and no longer a problem. (Is it, really?)
The next phase is of course the court cases, where authorities seek legal access to the data which is collected. Usually the police win these cases to establish legal precedent. Still - your average citizen is not reading civil rights-related or tech-related news, and they have no idea this happens.
By the time your average person finds out what the newly collected data is being used for, it's far too late to do anything about it.
Then there's the political aspect, which we are not likely to ever hear about. The boss's boss's boss's boss needs a favor done, don't ask why or for whom. That data, go get it. Listen, be discreet, no email and no cell phone. This is the one which is the most scary; an authoritarian in power who wants to target the opposition. Depending on the country, that could be a list of people who disappears and is never seen again - or in the US, gets raided over dubious charges by the local police as a form of harassment.
Argument two: Even if you can stop 100% the transmission of CSAM materials, you are not stopping the abuse of children. Just the secondary abuse of distributing the materials.