For instance, you'll often hear gun-grabbers say something like: “you don't need a gun like that for hunting”. If you respond directly to that statement (i.e. accept their premise), you've already lost. A better answer (no doubt, there are many better ones) would be: “So what? Where does the 2nd Amendment mention hunting?”
Another shifted premise I've noticed lately, has to do with the new e-cigarettes. Anti-smokers will say something like: “There's no evidence that these e-cigarettes help people quit smoking”. Again, so what? Hidden in that premise is the false notion that vaping tobacco is smoking. That's a duplicitous shifting of the definition of smoking. It's not smoking, it's vaping. There's no smoke involved — therefore, whenever someone uses an e-cigarette instead of smoking tobacco, he is smoking less. If they use e-cigarettes all the time, they have effectively quit smoking.
One of the most powerful tactics I've used in debate is the demurer. In your instance, I would reply, "You're correct. You don't need a gun like that for hunting. In fact, I would go further and say that you don't need a gun for hunting at all, or even hunting itself."
My opponent would stand there gaping, because I was supposed to fight the particulars of his assertion. Instead, I gutted his argument by NOT opposing it. It is simply irrelevant. Because I would go on to explain that hunting is immaterial to the right to bear arms, so that the type of weapon used in hunting is even less material.
In other words, I would concede his point about hunting, then demonstrate how the argument is not over hunting but the right to keep and bear arms.
Much the same as your response ...
In the health care debate, you constantly hear "Well, there are millions of people with no health care. Don't you think they have a right to medical care too?" To which the proper response is "Absolutely. I believe they should have the same right to medical care as anyone else. But this debate isn't about health care. It's about who should PROVIDE that health care. I assert that it is neither the government's right nor its responsibility to supply health insurance to its citizens. It may be a good idea, but that's not the point."
For instance, you’ll often hear gun-grabbers say something like: “you don’t need a gun like that for hunting”.
Would saying “I don’t recognize your right to decide what I need and don’t need” work? That’s usually my response when someone talks about my needs.