There's zero reasons to own those sort of guns. You don't need them for protection because a simple handgun fulfills the same purpose and you don't need them for hunting because a normal rifle can still get the job done. Using the argument of lunatics, they wouldn't even help fight off the government since the military (i.e. trained soldiers who actually know what they're doing unlike ignorant bumpkins) has the exact same weapons and more.

They serve no use to common citizens other than for weirdos to either feel better about themselves or so they can fetishize them.