@marcan I think for the OS bootstrap use case, curl|sh is totally fine. For installing apps though I think it's not only about trust but about scope: a script can do anything (including having a bug that deletes your entire disk), while most package installers will (more or less sanely) just place some files. Flatpak&co will even scope the file placement to a container. Now sure the installed app/tool can still have bugs, but I think limiting the scope of possible operations is always good.
@crepererum @marcan hum? Both rpm and deb packages can run arbitrary scripts as root on install without extra user intervention. Installing a package is giving root on your system to the package uploader.