And unfortunately that’s how arch is mainly marketed by its users. “Arch has the latest everything, if it’s not in the repos it’s on AUR” is one of the standard selling points.
Of course that speaks to how people use linux insecurely not how Linux is insecure.
Maybe most users just ignore that and always answer yes without inspecting it. I don't know. But the wiki for the AUR and Readmes for many of these tools have warning banners telling you not to blindly trust AUR packages.