Says who? A lot of gun owners have t-shirts and stickers which say things like "what part of 'shall not be infringed' do you not understand?"
They only read half of the sentence and assumed that was the complete second amendment. The full amendment reads "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." It implies that they need to be a well regulated militia to have this right and in fact both the background for the amendment as well as early supreme court decisions show this to be the case. It's also clearly not saying unfettered access to arms, only that they can keep and bear arms; would anyone want a sociopath to have a nuclear bomb or automatic weapon anyways?
There's quite a bit of info on wikipedia about the amendment which is worth reading if you find this topic interesting: http://en.wikipedia.org/wiki/Second_Amendment_to_the_United_States_Constitution.