To be clear the most critical arguments, against the dogshit they're putting into the world right now, have and must continue to center on harms to people and labor power. But I think it's still really important to point out, every single time, when their shit just doesn't do what they claim it does, especially when it has no clear path to doing so in the future. Tech capitalists are used to not being called on this. Most of the media is eating out of their hands, they've developed these rhetorical reflexes that we've all come to recognize from years of uncritical coverage: "Soon, this could be everywhere", "Right now it can only do X, but you can easily imagine in a year or two's time...", "It may not be ready for prime time yet, but...", etc.
And the thing is, tech capitalists ultimately don't even care whether or not what they're selling does what they claim it can. But calling bullshit hurts their sales pitch - and with enough people doing it loudly and well enough, it can truly shift the rhetorical power balance in a given situation.
The recent Amazon "actually just a bunch of exploited workers" potemkin AI store bullshit was apparently aiming for only 50 out of every 1000 transactions needing human intervention. They didn't get below 700/1000. That shit was never going to happen, it was a pure fantasy by some executives giddy with the profits they projected if they could cut workers even closer to the bone, and roll that out as the Future of Retail, everywhere. But you know right up until they bailed, they were out there pointing to The Numbers (fudging them as needed, as one can always do with numbers when ethics are of no concern) and being like "see? our very sophisticated very cool Machine Learning is getting better and better at detecting stuff. why, in just a few years, it'll be pretty close to perfect!" (do not use this as a drinking game phrase. you will die.)
So I think it's very important to bolster our central arguments - that this is a power grab for the future of humanity, perpetrated by capitalists who are wielding tech to exploit and control us - with the plain truth of technical critique, which is that in a vast majority of cases they are making wild extraordinary technical claims that do not hold up to scrutiny and that they are presenting without sufficient evidence. If you are a person knowledgeable in technical matters, this is a good use of the authority society has pretty much automatically granted you. Be rigorous, of course: ask for proof, point out flaws and discrepancies, distinguish marketing from reality. And be comfortable with the inherent ambiguities of forecasting: don't bother making a specific counter-claim unless you're nearly certain of it. The most important thing is to displace a tech capitalist's claim as the sole word on the matter. In a better world, people would default to doubting every single word out of these companies' mouths. This edge of the Overton window already has a nice handle on it.
The biggest reason I think the past few hype waves have swept up so many people and had such far-reaching negative impacts is that the tech industry has secured this implacable position in the public mind, creating self-amplifying cycles of both positive (the yearly PR rituals, product launches etc) and negative reinforcement. Most media people still live in absolute terror of being the next "guy in 2007 who said the iPhone was going to flop" - the world they operate in means they will never be punished for being too credulous but punished severely for not being credulous enough (ie being critical).
Tech has seized the entire territory marked "The Future" in the popular consciousness, and they've shown us very clearly what they intend to do with it. They're going to be capitalists, they're going to make our lives as precarious and powerless and miserable as possible as they further concentrate all wealth and power. Fighting to reclaim the future from them will be a generations-spanning project, and we have to get good at firing every effective weapon we have. The general public will pick up on this, the "techlash" is getting more and more mainstream every year. We can win this, but we have to go for the throat.
