I want to clarify something: When I wrote that I didn't buy the tyranny argument, that does not mean that I don't recognize that tyranny can't occur. You mention the Bonus Marchers, and Japanese Internment, and there are plenty of other examples in this country. (I don't think Ruby Ridge is one of them, but that's a personal opinion.)
What I don't buy is that private gun ownership deters tyranny in any way. I get that, in your opinion, that was the original intent of the 2nd Amendment (this is certainly not a universal opinion by any means) but even if it was the original intent, it no longer applies on a practical basis.
Sometimes humor is the best way to demonstrate why people might think a particular position is absurd. Please read the following Onion article. It may offend some of you, but it really does represent what a lot of the public think about those who stridently hold your opinions about tyranny and private gun ownership:
http://www.theonion.com/articles/62yearold-with-gun-only-one-standing-between-natio,30984/