What I don't think you foreigners get is that when someone replies with '2nd Amendment says so' to a question about why they own guns, it's a very polite way of heading off a debate and at the same time telling you they do not want to be bothered on the topic. Basically, it's a polite way to say mind your own business. They don't feel the need to justify themselves anymore than you do when it comes to your love life, your job, the color of your hair or any of the other myriad life choices you make on a daily basis that you don't want to be questioned on or about. To them, owning a gun is as natural as it is for you to own a car. It's not weird. It's not something they feel they should have to rationalize and justify to you, and efforts to do so just exasperate them.
Using the same car example, how would you feel if an environmentalist walked up to you as you were about to start your car and started questioning you about why you weren't using mass transit, or riding a bicycle or walking instead of polluting the environment and potentially causing someone to die or be physically impaired by your carbon monoxide emissions. You'd feel uncomfortable, yes? I'd tell them to fuck off. A more polite person might point out that there is no law limiting their freedom to possess and own a car for transportation. What if that environmentalist then went to the government and tried to have cars banned from the road? Would you be pissed off, or would you just go along with it?
Oh Jay, that's such a stupid example, cars can't be used for mass murder. More people die in car accidents every day from careless drivers than die in gun related incidents every year. Even with general licensure requirements, insurance requirements, seat belt requirements, speed limits, stop signs, etc. people still die. We take car accidents as part of living in modern society and, while we might dread it, it's not something we really worry about and it's not something the news even bothers reporting on unless it's a minivan packed to the gills with small children. Shootings make the news because they are more rare. Because they are so rare, it's largely a waste of time, effort and breath to try to ban them. It's like using a pebble to stem the tide of a river. People die. Kids dying in a school is a tragedy. Move on.
Now, as for guns themselves, well, it's not just the 2nd Amendment that props up private gun ownership, it's over 200 years of case law as well as multiple instances of the Supreme Court upholding and strengthening gun rights. The NRA has been the chief advocate of gun rights and gun owners for a while now, and you have to understand that in many cases they take what appears to be an extreme position, but it's just a negotiating tactic. If they take that extreme position, they end up with a more favorable outcome when gun laws do get placed on the books, one that is more to their side of the thought process than to the people who want them banned. They've advocated for gun control laws in the past, they've pushed for local background checks, and safety courses for concealed carry permits etc. They aren't the enemy by any means. Honestly I wish there was a well funded group that stood up for the other amendments just as heartily, but all we have is the pussy ass ACLU and their band of well-meaning misfits.
Lastly, regarding the lines about tyranny to justify gun ownership, it's an argument that is definitely on the weak side, but it all comes from a few famous quotes that Americans have had over two hundred years to digest and pass down.
"The very atmosphere of firearms anywhere and everywhere restrains evil interference - they deserve a place of honor with all that's good"
-- George Washington, 1st US President
"God forbid we should ever be twenty years without such a rebellion. The people cannot be all, and always, well informed. The part which is wrong will be discontented, in proportion to the importance of the facts they misconceive. If they remain quiet under such misconceptions, it is lethargy, the forerunner of death to the public liberty. ... And what country can preserve its liberties, if its rulers are not warned from time to time, that this people preserve the spirit of resistance? Let them take arms. The remedy is to set them right as to the facts, pardon and pacify them. What signify a few lives lost in a century or two? The tree of liberty must be refreshed from time to time, with the blood of patriots and tyrants. It is its natural manure."
-Thomas Jefferson, 3rd US President
“Americans have the right and advantage of being armed - unlike the citizens of other countries whose governments are afraid to trust the people with arms.”
― James Madison, 4th US President
So, yeah, that's where that line of thinking stems from. Call it outdated, call it stupid, call it whatever you want, but it is enmeshed in the fabric of what it is to be American. Good luck changing that, or convincing most people to think otherwise.
"Ah, you miserable creatures! You who think that you are so great! You who judge humanity to be so small! You who wish to reform everything! Why don't you reform yourselves? That task would be sufficient enough."
-Frederick Bastiat