In the most general sense, "why I carry a gun" is a philosophical statement. We, as a civil society, have come the point where we expect a lot of things to be provided to us by our government: security and personal protection, medical care, retirement benefits, etc. As our society becomes demonstrably less "civil", less moral, infiltrated by illegal immigrants who are "outside" of any American law, especially in the southwest and larger cities, and the whole mix is stirred by financial stress from an economy that is tanking, the likelihood of an encounter with a violent or potentially violent criminal escalates.
The sad truth is that even though we may have some of the most dedicated, honest, brave and committed law enforcement civil servants, the task at hand is daunting and crime is on the rise. Our courts, prison systems and law enforcement agencies are being overwhelmed. To reasonably expect nearly instant response from law enforcement, or absolutely safety in all public situations is as naive as the notion that your medical care and retirement needs will be provided by the state. The mechanisms and institutions are in place, yes, in theory, but they can never entirely cope with the task at hand.
A lawless society is a frightening thought. But to the extent the American citizen has become entirely content to rely on someone else, some state institution, to always protect them, as a substitute for upholding a personal code of ethical and moral behavior and self-reliance as our first line of defense against a lawless society, to that extent we place ourselves at risk.
Teach your children well. Understand that the Constitutional right to bear arms is meant to facilitate self-reliance in protecting yourself, your family, your property, and your country, if needed. But it comes with the Constitutional understanding that we are a God-fearing nation of laws and personal responsibilities. Those laws are both "Natural", endowed by our creator -- life, liberty, pursuit of happiness, and derived by our legal system and government by and to the extent that we, as individual citizens, entrust that power to our government. Support law enforcement, obey the laws, but always be ready to protect yourself and others in a lawful and prudent manner, if that is what is required. But never surrender or abdicate your own personal responsibilities and self-reliance, or else you voluntarily assume the role of the victim, and the victim mentality.
Praise the Lord, and pass the ammunition.