One of the biggest questions/arguments right now by both those who wish to disarm us as well as those who simply don't understand the issue is why does anyone need an assault weapon? Despite the fact that we don't have to show a need to execute our rights, it's a question that I think people deserve an answer to. After all, firearms can be very dangerous in the wrong hands, so it makes sense that people not familiar with the issue would want to know why ordinary citizens should be allowed to own them. I get the impression that a lot of people on our side of the debate consider the very question to be distasteful, and how dare anyone question us as to why.
Reading articles, watching interviews, etc. where intelligent, well spoken people are asked this question, they have typically responded that we need them to defend against a tyrannical government. While this is true, and something the founders had in mind when they recognized the right to bear arms, it's an argument that the opposition can very easily spin to make us look looney or paranoid. Instead of jumping directly into this argument, I think there is a better and much more digestible answer:
I need the ability to own an assault weapon because the constitution of the United States says it's necessary for the security of a free state.
There are multiple ways to explain how the 2nd Amendment applies to so called "assault weapons", most notably the recent Heller ruling where the meaning of the term arms was examined and determined by he Supreme Court. We can speak to defending against tyranny as one example as to why the constitution states we need to right to bear arms, but the best and first answer to the question of why we need the right is that the constitution states that it is in fact necessary for a free state.