The BSDs prevent this by never having allowed random jamokes to upload Makefiles into the ports system.

Yeah, I've prevented this locally too by never building such a platform in the first place, always the best solution!

Jokes aside and just in case, you do realize ports and AUR have two very different models? Ports is more similar to the official Arch repositories, which obviously doesn't suffer from the same problem, and AFAIK, there is no BSD-equivalent of AUR.

BSD is cool and useful for lots of reasons, but comparisons based on misunderstandings helps no one :)