It makes Automatic weapons readily available to people that will misuse them. Giving someone a 3 shot shotgun and giving them a 200 round box of belt fed ammo in a GPMG are 2 very different things.
1 has practical uses, ie hunting. 1 does not.
Machine guns are prohib fora reason, there are however lots of rifles that should be non restricted that are either restricted or prohib. I have no desire to see FA rifles and machinguns become legal. They only give people more firepower than is neccissary for a civi to have. If someone breaks into your house a shotgun or rifle is fine for self defence, there's lots of semi auto's out there. Full auto only gives you cover fire from combat situations for killing other humans in time of war.
I would LOOOOOOOOOOOOOOOOOVE to own a FA assault rifle, but that means that store need to sell them which creates a much bigger pool of incredibly devastating weapons for criminals to choose from. When crims have easy access to the same weapons that the military and police use, you're only asking for trouble. It only makes me feel less safe.
Most people Im sure would be responsible, jsut like most gun owners are. But instead of a guy walking into a school and shooting shotguns at ppl, now you start to get into people bringing machine guns to shcools and killing dozens and dozens if not hundreds of people.