> If you install unvetted packages in your airline control system, bank, or supermarket, the kind of systems that we're talking about here, you have much bigger problems to worry about.
Surely we can agree that if it's a vector with an above 0% chance of it being exploited, then any methods for mitigating that are a good thing. Quite possibly even multiple overlaid methods for addressing the same risks. Defense in depth and all, the same reason why many run a WAF in front of their applications even though someone could just say: "Just have apps that are always up to date with no known CVEs".
> Or indeed any of these. Highly privileged users piping shell scripts from untrusted sources is out of scope for any antivirus system, on any platform.
You don't even have to be highly privileged to steam information, e.g. an "app" for running some web service could still serve to exfiltrate data. As others have mentioned, maybe this is not what AV software has been historically known for, but definitely there are pieces of software that attempt to mitigate some of the risks like this.
I'd rather have every binary or piece of executable code be scanned against a frequently updated database of bad stuff, or use heuristics to figure out what is talking with what, or have other sane defaults like preventing execution of untrusted code or to limit what can talk to what networks, not all of which is always trivial to configure in the OSes directly (even though often possible).
I won't pretend that AV software is necessarily the right place for this kind of functionality, but I also won't pretend that it couldn't be an added benefit to the security of a system, while also presenting different risks and shortcomings (threat vector in of itself or something that impacts system stability at worst, or just a hog on the resources and performance in most cases).
Use separate VMs, use secret management solutions, use separate networks, use principle of least privilege, make use of good system architecture, have good OS configuration, use WAFs, use AV software, use scanning software, use dependency management alerting software, use static code analysis, use whatever you need to mitigate the risk of waking up and realizing that there's been a breach and that your systems are no longer your own.
Even all of that might not be enough (and sometimes will actually make things worse), but you can at least try.