That is the crux of the argument. I realize that U.S. constitutional protections apply to the government only, not private entities like Apple. However, from my very much layman's perspective, it appears murky, since Apple would be acting as a government proxy.
Thus far, us tech enthusiasts have been relatively unscathed from government interference. The only notable government prosecutions were a failed attempt by the DOJ to break up Microsoft, and a toothless FTC settlement with Intel, which was years ago. As limited as those actions were, what impact they did have was on those specific corporations, and not the end user.
That's changing, with governments around the globe targeting "Big Tech", which seem to be primarily U.S. based entities, including Amazon, Google/Alphabet, Facebook/Meta, and of course, Apple. I'm sure there are politics at play, perhaps with the EU's aggressive stance being notable. I would also note that, at least in the U.S., Microsoft bought its way out of anti-trust legislation. The bills working through the House Judiciary Committee originally had language that targeted all operating systems, but that was re-written to specify mobile operating systems. This was done after Microsoft Vice Chairman and President, Brad Smith, gave the maximum bribe...err, donation to the campaign of Representative David Cicilline, who is Chairman of the panel overseeing such matters and co-sponsor of the most prominent legislation making the rounds through the House or Representatives. (I would note that this is bi-partisan, so equal responsibility goes to both major U.S. political parties.)
Politics aside, I realize that there isn't going to be a purely libertarian solution to this, and at some point, sooner rather than later, governments are going to put a great deal of pressure on Apple and other large technology companies to find solutions to the CSAM issue. The old "think of the children!" straw man always wins, because nobody wants to be seen as siding with abhorrent abusive criminals. I realize that blocking such regulations is unlikely, so I'm curious how Apple and other technology firms will ultimately address the situation. There may be some level of preventative measures provided by the U.S. constitution, but most tech companies are going to want a singular solution, which is what Apple was working on. Apple, nor its developers and users, want product editions of an iPhone or Mac that depend entirely upon the jurisdiction of the region in which the customer lives in.
I think Apple could have done a better job in explaining their reasoning and implementation, but I'm not certain Apple is willing to directly come out and say that they wanted to do this before governments forced them. Apple's solution, as much as privacy advocates dislike it, is going to be more privacy-focused compared to what some ham-fisted politician or tech-illiterate bureaucrat believes is in the best interest of the public. I think Apple's secrecy probably hurt them in this case, got caught flatfooted by the negative response, and should have at least attempted to consult organizations like the EFF, but they botched the rollout, thus hurting both themselves and their customers. Perhaps nothing would sway the likes of the EFF, but some level of support from advocacy groups would have been welcome. Regardless of what ultimately arrises from this mess, I trust Apple more than the likes of Google or Microsoft to protect user privacy, but there's only so much they can do about "I'm from the government, and I'm here to help" mandates.
As always, thank you for the thoughtful commentary and perspective,
@Cmaier, much appreciated. I like to think of myself as a realist, like most folks here are, and that this issue is going to be forced upon us, whether we like it or not. At this point, trying to find a compromise solution that doesn't destroy "privacy is a fundamental human right", as Tim Cook often says, and satisfies government mandates is the best we can hope for. Do you have an opinion about where Apple takes this from here, or do you think they'll just wait for governments to force their hand, essentially Apple will say "we tried, but you didn't want it, so now the wise folks in government are doing it for us"?