EDIT: My post was meant in reply to lil weasel's post about the necessity of guns for national defence, not Irviding. Apologies for the confusion.
@lil weasel: Alongside Sivi's very good points, I'd just like to add my two cents on the shortcomings of your pro-gun arguements. It is short-sghted by both parties in the pro-gun vs. anti-gun camps to boil down gun ownership to only their advantages or disadvantages - something I feel you are doing. There are good and bad things in gun ownership, and you have to balance out the good versus the bad.
Regarding civilian gun ownership and national defence - I'll point out that the likelihood of the US being wholesale invaded by any other nation anytime soon is frankly laughable.
Gun ownership might give civilians-turned-insurgents a few extra weeks headstart in defending their country - but not much else. Two personal cases below:
- I visited Syria in 2010, a year before the revolution, and virtually no one had guns. No even the security protecting the airport - in fact they didn't even have melee weapons - they only had their shoes or belts as weapons if the worst happened. Now the country's awash with international black-market weapons and those captured from the army.
- In the year prior to the 2003 war in Iraq, the government started arming every household with automatic weapons, with free training of civilians in guerilla warfare and sleeper-cell operations. Yet not a single bullet was fired against the oppressive dictatorship until the Coalition forces disbanded it, in which case it was Iranian-sponsored militias.
My point is that defence of a nation depend far more on the will of the people than on guns alone. And the massive international black market is always happy to help all those committed enough toorganise and raise funds.
Your point on the advantages of guns in protecting America are thus over-exaggerated on two fronts - the likelihood of invasion, and the usefullness of civilian gun ownership.
Now, regarding the disadvantges of civilian gun ownership IMO:
Easy gun availability to the civilains means easy gun availability to criminals. Now before anyone throws the typical pro-gun arguement "criminals get their guns on the black market":
- The US guns black market is fed from legally brought guns, via 'straw-purchases' (PBS Frontlines). In fact, even the black markets in neighbouring Mexico and perhaps beyond are fed by legal US weapons. It is simply far easier than dealing with, or stealing from, militaries.
- Many criminals still buy their guns completely legally. Only because they are criminals, does not mean they do everything in their lives illegally - most criminals legally buy their cars etc...
Secondly, I simply do not believe that civilians without professional training, authority and responsibility (i.e. armed law enforcement/military) can be trusted with guns.
I do believe people have the right to defend their lives in any way possible - including crimes like murder. However, put a gun in that same civilian's hands, and they are far more likely to pull the trigger out of fear or anger at those who do not pose a direct and immediate risk to their lives. They are also likely to shoot at the criminal before exhausting all other options available to them.
And finally, even if you believe that it is ethically justified to shoot a guy dead simply because he entered your house, or looked at you the wrong way on the streets, you have to consider escalation. If he has a gun too, the situation will likely end up with one of you dead. And over what, a few thousand dollars worth of jewelry or a stupid arguement in the streets?