Let’s say, for example, that I invite a friend over and offer them a glass of water. Would you be similarly upset to find that I don’t recommend that they first send a sample of the water to be tested for purity before consuming said glass of water? I mean, don’t get me wrong, I would be fine with my friend being cautious and wanting to get the water tested (though I doubt that would ever happen in practice)… but if he trusts me to give him clean water, I doubt you’d raise any fuss over him just downing a glass.
Why/how is this any different? Anyone that wants to inspect the shell script can amend that line to first save and view the script. Are you thinking it’s never appropriate to trust such a script implicitly? If that’s the case, I’d love to hear about your workflow for checking the packages you install (e.g. debs can run arbitrary post install scripts, and do you know that a malicious actor with signing keys didn’t taint the binaries therein?), how you inspect all JavaScript for sandbox escaping exploits before viewing anything on the web, how you’ve ensured your hardware itself isn’t backdoored, etc.
The complaints of piping directly into shell from an HTTPS server strikes me as nothing more than a “no real technologists does $THING!” sort of elitism, though I’m open to being shown otherwise. A non-answer would be to propose that one first fetch a package signing key and install from your package manager of choice — if the script we’re complaining about can’t be trusted, there’s no reason to trust that the key file is any better with it being hosted in exactly the same way… unless you’re going to propose that you use something along the lines of web-of-trust to inspire further confidence that the signing key is authentic; at that point, though, your problem is with how 99.9% of third-party software packages (with respect to your distro of choice) are distributed - every PPA I’ve ever seen (docker, mongodb, whatever) at best tells you to fetch a key from some HTTPS server, and that’s all. It would then strike me as suspect to single out curl|bash (while additionally implying something about Rust users).