Grant Cunningham raises a good point in his recent essay, The concept of 'need'.
If a prohibitionist asks why we "need" something, he is presupposing that the exercise of a fundamental right is contingent upon showing good reason to exercise that right. The idea that humans have rights simply because they exist is completely bypassed, and the concept that rights are something a government confers upon subjects is cemented in the very structure of the question. By answering, in any form or manner, the question of need we tacitly accept their premise that rights do not exist beyond what someone else is willing to allow. Even entertaining the question plays into their trap.
I agree that letting the antis frame any part of the debate is a bad idea. Do not let your opponent talk about "need" until he or she first agrees there is a fundamental right to effective self defense. Emphasize that "effective" in this case means that the victim will have an equal or better chance than the criminal of escaping the encounter unharmed.
Frankly, I don't think the anti's even care about what you "need" because they don't believe you have any right to resist criminal attacks. That is why they always argue, "Just give them what they want." The "need" argument is just a rhetorical trick to move the debate to a place where we can be attacked. Concentrating first on the civil rights issue gives you more leverage. The anti's don't want to talk about rights because, deep down inside their scabby little souls, they just hate guns and the culture that guns are a part of. I am convinced they seek the deliberate and systematic destruction of the entire unique "gun culture".
Another part of the "need" debate that, I think, works against us is the assertion by some gunnies that a percentage of bullets fired by a defender in a typical self defense scenario will miss their intended target. That may be true and the figure I see tossed around a lot is 70% to 80%. That means, on average, seven or eight of every ten bullets fired will miss.
Now look at that a from an anti-gun point of view.
"Oh My God! You need high capacity magazines so you can miss seven times out of ten? Do you think those bullet are just going to disappear? No, they are going to hit something or someone else. You must be some kind of irresponsible idiot to be willing to endanger innocent bystanders just so you can feeeeel safer."
Unfortunately there have been some recent high profile police shootings where bystanders were injured by stray bullets. These help reinforce the anti-gunners' perception that gun owners are irresponsible loons so be careful.