2nd Amendment: A well regulated militia being necessary to the security of a free State, the right of the People to keep and bear arms, shall not be infringed.

I read nothing in this statement that would prohibit an individual from owning any armament he chooses. Individuals in 1778 could, if wealthy enough, own the most advanced weaponry the world had to offer. Why should it be different now?
Perhaps, because we might have to live with its consequences.