AUR (also PPA which another comment cited) is
emphatically not the same as "just run this script". If anything, and at worst, it's analogous to NPM: it's an unverified repository where the package is run at the whim of the author, and it leaves you subject to attacks against or by that author.
You still, however, know that the author is who they say they are, and that other people (the distro maintainers) believe that author to be the correct entity, and believe them to have been uncompromised. And any such compromise would, by definition, affect all users of the repo and presumably be detected by them and not by you in the overwhelmingly common case.
"Just run this script" short circuits all of that. YOU, PERSONALLY, ALONE have to do all the auditing and validation. Is the link legit? Did it come from the right place? Is it doing something weird? Was the sender compromised? There's no help. It's all on you. Godspeed.