I would go through manually installing dependencies and setting up my system, adding repos, etc. over running some script any day. But then again some projects wouldn't be that popular if they were hard to install.
Some of npm's installation instructions ask you to pipe curl into bash, to run a lovely script [0] which makes things easier for you, but not by much. Is it really necessary? Would developers give up trying to get npm and node just because installing not as easy as "curl https://some.script.com/that-script.sh | sudo -E bash -; sudo apt-get install npm"?
Other than building/installing programs, adding GPG/SSH keys like in the blog post can be as dangerous, and while not simple, there could be some method built to make things easier without having to run commands you don't even check.
Anyways, hope projects grow out of this habit.