[TangoTrotFox]

Everything only has value that people assign it. I think paying some thousands of dollars for a handbag that has a certain label, or paying $1000 for a phone with a certain label, or so on is completely irrational. But in a market economy, I don't get to decide - the market does. And there's no irony using dollars in that example, as once again they face the same problem. The value of a dollar changes quite regularly against other currencies and it's just a market supply:demand reaction. Should the petrodollar end, I'd expect to see the dollar plummet globally. Great for our exports if our economy doesn't go down alongside the dollar!

51% attacks in Bitcoin are not a real risk for two reasons. The first is that it'd be completely illogical. If there were a group of miners able to work together to generate the resources sufficient to obtain a 51% attack on a major coin, they'd already be printing massive amounts of money completely legitimately. If they started trying to use that to do things like double spend, that'd ruin all of this because of the second point.

Bitcoin is decentralized. And if one branch becomes broken because of something like a 51% attack, it is trivial to fork it and go. Bitcoin Cash being the obvious example of this, and that was over something that lacked a unanimous consensus - nobody is going to want to stay on a fork that's been compromised.