1. Because firearm ownership allows you to take a proactive stance on self defence and crime prevention. Fear is not a state of being that any free person, let alone an American, should live in. Accepting defenselessness is not acceptable.
2. Gun ownership is a part of the system of checks and balances designed into the Constitution by its framers. An armed populace with effective weapons keeps a government from becoming too powerful and oppressive. This was how America was formed, and thus was included in the Constitution in case the need ever arose again. It is no mistake nor is it coincidence as to what order the amendments fall in. As a teacher of mine would say "The Second Amendment defends the First."
3. The best argument of them all in my opinion: tyrranical governments love a disarmed populace. Nazi germany: Jew, gypsies, and all others not of the 'master race' were herded onto trains and slaughtered like so many sheep. Gun control preceded this and was designed to enable it. Stalinist USSR: millions were shipped to Siberian labor camps to die. Gun control enabled this. The United States, Reconstruction era: the Second Amendment rights of newly freed slaves were abridged, enabling those who were in power prior to the ending of slavery to hold blacks in place through fear, intimidation, and murder. History is full of examples of why gun control not only does not work, but is dangerous to the freedom of a nation. Those who do not learn history are doomed to repeat it.