The second amendment should be about defense in general and not about the need to own specific things (arms, weapons, guns) used for the act of defense.
1) The Bill of Rights amendments apply to all people, but 2A applies only to a subset of people. One never loses the right to free speech or religion or assembly, even if you have committed a felony. 2A is not a natural right like the others in the Bill of Rights
2) 2A gives an unfair economic advantage to the arms industry. All other things that could be used in defense of self or property do not enjoy that political support
3) the use of arms for sports or collecting hobbies should not be a protected right. They are not natural rights like freedom of speech, etc.
4) Individual ownership of weapons is not needed to defend the state.



