Assault weapons are not for hunting, or even for personal self-defense. Assault weapons are for war. Their purpose is to kill as many people as possible, as quickly as possible.
Who could agree that such weapons should be available to any person 18 years or older, walking into a store to buy one without any background check? Indeed, to anyone? Second Amendment rights were not intended for automatic weapons — they had not yet been invented.
If someone feels the need to operate such a weapon, let him or her join the military. They will offer you that opportunity and even supply your ammunition.