Comment by Zak

It is also common for people to install things on Windows without thinking critically. It is perhaps less common on Mac OS, but I've seen someone get malware that way.

My position is that this is not the OS vendor's responsibility to prevent. A warning is fine. A scan for known malware by default is fine. Beyond that, it's my device and it's my choice to get software from wherever I damn well please even if it might be a bad idea.