Install scripts for what exactly?

Majority of software is packaged natively.

Why not? You (usually) just click the check box during install, and you have 1 extra password when you boot up your system. Doesn't seem too hard but I might be missing something.

They should not us LUkS and instead use veracrypt for folders and files. That way if any repartitioning or modification is needed it's simple in gparted or GNOME disks on mint.

Source is been there and done that. Luks partitions are not easily resized.

Is there anything stopping viruses from doing virus things?

Usually that's called sandboxing. AUR packages do not have any, if you install random AUR packages without reading them, you run the risk of installing malware. Using Flatpaks from Flathub while keeping their permissions in check with a tool like Flatseal can help guard against this.

The main difference is that even with the AUR being completely user submitted content, they're centralized repositories, unlike random websites. Malware on the AUR is significantly less common, though not impossible. Using packages that have a better reputation will avoid some malware, simply because other people have looked at the same package.

There is no good FOSS Linux antivirus (that also targets Linux). Clamav "is the closest", though it won't help much.