They are an important tool in America's system of checks and balances: Guns are not for shooting deer; guns are for shooting politicians.
The 2nd Amendment is very clear; in fact, it's probably the clearest portion of the entire Constitution:
"A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed."
In order to protect the freedom of each state from the imposition of some tyranny, it must be possible to gather groups of patriots who are armed with the highest quality equipment; therefore, the right of the people to keep and bear arms shall not be infringed.
America was born out of armed revolution against a tyrannical government, and Americans are taught that they must be wary of enemies both foreign and domestic. To Americans, the government is at best a dangerous servant, and at worst a tyrannical master.
The gun is known as "The Great Equalizer" for a reason. To restrict gun ownership is to transfer even more power from the weak (the individual) to the strong (the State); that is anathema to those who understand what it actually means to be an American.