We have a right to possess something not because we need them but because the government has no moral right to punish us if we have them. The basis of this Republic was to limit the criminal authority of the state only to those functions which are justified to punish malicious or outrageous acts.
As for the 2nd Amendment it is intended to secure the rights of the states to possess their own militias. That's what the Amendment refers to. Clearly the purpose is so that each state can defend itself, but from what, other states or the Federal government? Seems the Civil War put an end to that Right..
But what's implied in the 2nd Amendment is that all citizens would have weapons because a militia is a group of citizen soldiers using their own weapons. It's an archaic idea now as the states have National Guards which supply the weapons, and helicopters, and tanks. But nevertheless the idea that the Federal government could come along and restrict the ability of citizens to possess weapons would have been unheard of -- ridiculous. There would have been no need for such. But then the idea of mass shootings would also have been considered unheard of and absurd.
The point of the 2nd Amendment was not to guarantee individual rights to possess weapons but for the States to have their own citizen armies to defend against other states or the Federal government, and the Civil War destroyed any legitimacy of a State resisting Federal authority with force, EVEN IF that state voted solidly to do so (which was clearly the intend of the founders).
But the 2nd Amendment has been twisted in order to preserve this individual right as many important things like privacy have been found, through twisted interpretation, to be present in the Constitution because it's easier to do that than to Ratify another Amendment to clarify that Right.