Buttcoin

There's also a massive overlap between rationalists and libertarians because a fundamental belief in the supremacy of your own mind, with its attendant presumption that the vast majority of people are incredibly stupid because they don't agree with you, tends to align very strongly with individualist philosophies.

This is absolutely true and, I think, is also the core answer to OP's question about why rationalists love cryptocurrency.

Because the core conceit of Bitcoin, and everything that followed, was the idea that you could "be your own bank" - that you would have complete control over, and complete responsibility for, your own financial transactions. If you get hacked or scammed, or send your money to the wrong account, or lose your private key, or forget your password, there's no bank or government you can appeal to to fix the problem. Once cryptocurrency is gone, it's gone for good.

And to be clear, this is cryptocurrency working as intended - independently of the scams and the bullshit and the obvious fact that cryptocurrency is based on nothing but people's belief in its value, the fact that erroneous cryptocurrency transactions cannot be reversed is a feature. It's a selling point.

For normal people, this is obviously a horrible idea, because normal people recognize they can make mistakes and want to be able to fix those mistakes, especially when they involve things like their life savings.

Libertarians and rationalists and their ilk, on the other hand, don't really believe they can make mistakes. They think other people are stupid and irresponsible. Other people could screw up and lose their money. But the libertarian, with his superior mind, does not fear making a mistake or becoming the victim of theft. He's too smart for that. His confidence in himself is boundless.

So the libertarian doesn't need the safety net of laws and governments and banks and credit agencies that protect the average person from theft and error. When the libertarian is told he can be his own bank, and save his wealth in a format designed for irreversible transactions, where one mistake would lead to his wealth disappearing forever... well, the libertarian thinks this is a great idea, because he doesn't believe he would ever make a mistake.

You have to think yourself very smart indeed to be that stupid.