If you follow that to it's logical conclusion then "everything is terrible and nothing is secure" (which is probably the reality)
My personal gripe with piping curl output to sh is about expectations. If I have some binary I'm running, I have _some_ expectations about what it will do, same for a Makefile, and RPM, etc. None of those things are guaranteed to do what they're supposed to but I have some idea what _should_ happen.
Unless I read through the script, I have less expectations about what the script is going to do. It says it will install my program but is it going to pull in dependencies from my package manager? Download and compile something, shove binaries in my $PATH, edit dot files in $HOME?