In all the years I've used the AUR I only heard of one pkg violating security, it was recognized pretty fast and was removed within hours from going up. AUR pkgs have history/track/votes on them, with thousands using them it is just as likely an official pkg having rogue code as an aur pkg.
Also, aur pkg are not really software written for the aur, it is software packaged for the arch ecosystem, and several other distros are using them.