Why do you need internet access? Why are presses allowed to be sold unlicensed? Why are churches not forced to adhere to federal standards of religious conduct?
We have certain unalienable rights that are recognized and guaranteed in the Bill of Rights. The Right to Keep and Bear Arms is one of those rights. That right does not say 'only flintlocks', or 'only things that don't look scary'. Assault Weapons, or really the semi-automatic firearms you and the media mistakenly call Assault Weapons, are arms.
With that logic we could have nuclear weapons. There have to be some sort of limits.