Well, first of all, nobody with a conscience should dignify that question with a response. I will just for due diligence; but, the question tells us immediately that the person who is asking doesn't believe in freedom. If you believe in bans on anything the burden should be on the government to prove why we don't need the thing and why it's necessary to keep us from it. Shifting the burden on citizens is to run on the assumption that the government can ban whatever it wants until the people convince them of a need. Freedom doesn't work that way and it can't.
It's the Bill of Rights, not the Bill of Needs.
Still, to dignify the question with a response, it's still a dumb question and you're gonna get a lot of answers that you don't like.
I neither need nor want a .22 calibre rifle. I'm not gonna use it for home defense. It's not gonna be useful for me to train on before I grab my 30-30 and go deer hunting. I have no use and no need.
Why do I need a 9mm handgun? Well, I don't want one. I think my next gun is gonna be a revolver that takes .357 magnum. I know plenty of people who have them and there are plenty of needs. If you're being assaulted, they're easy to use and effective and they can carry a lot of rounds.
Why do you need so many rounds? Well, adrenaline in itself is a powerful thing and there have been cases in which an armed criminal has been hit eleven or more times before the fight stopped. You add drugs and alcohol into the body of an aggressor, you might need a lot more bullets before the threat is neutralized.
Why do you need an AR-15? Well, do you think that every home break-in is committed by one dude? Do you think every robbery of a convenience store robbery at 4am only has one assailant? During riots when people are looting and lighting homes and businesses on fire, do you want a handgun or a rifle?
Why don't we get more specific? Do I need my 30-30? Well, I've never hunted in my life; so, my argument for needing my Winchester doesn't apply there -- I've only used it for recreation and entertainment purposes. Arguably, that round has taken down more down than any other in American history; but, is the government going to approve each round for each individual based on need? Is, "I need it for a movie." not an argument?
Why do I need a 45-70 round? Well, I definitely don't. People who work in the Alaskan wilderness face the possibility of grizzly attacks every day -- they need it. That's why federal laws working off of this manner of thinking are all bullshit.
Still, we all need guns as a check against the government. We need an armed citizenry to keep the government scared. This shows you how pro 2A people have already given too much ground. We've compromised and you keep pushing harder and complaining that we won't compromise.
We shouldn't have compromised at all because we're arguing for rights and you're arguing for control. We let you flip the burden on us before I was even old enough to get into the fight and we never should have let that happen.