You can't measure the stability of a currency just by comparing it to your own currency. If we followed that line of reasoning, the only stable currency to you would be one which is pegged to the US Dollar. The price of one Euro fluctuates if you measure it in Dollars, yes, but that does not speak against the stability of the Euro more than it does against the stability of the Dollar.

Nobody can enforce the value of anything. At most, central banks have the power to avoid their own money to be overvalued, by using the printing press and selling their own money in the market. But this is just a one-way power that does not work in the opposite direction: If the market decides that your currency is not worth what is worth, you will run out of dollars (or whatever foreign money you have) trying to buy your own currency to "sustain" it before you can convince the market otherwise. As bitcoin does not have a central bank, and more importantly, bitcoin is not a fiat currency that you can make out of thin air, your idea of "buy and sell bitcoins" is fatally flawed.

This is not "your commit privileges are revoked".

They are using git, so this is "I'm not pulling changes from you" instead.

No "chain" here. This is not SSL, this is GPG, and the term used here is "web of trust". To consider the web of trust broken you would need to find that one of those fake GPG keys is signed by someone you trust.

Exactly. This is from the nautilus-dropbox Debian package available in non-free:

Installing this package will download the proprietary dropbox binary from dropbox.com.

That's far from being free software, unfortunately.