If you go back and read what people thought about money in, say, 1870, there was a time that the notion of purely paper currencies was widely held to be the sam

If you go back and read what people thought about money in, say, 1870, there was a time that the notion of purely paper currencies was widely held to be the same sort of absurd folly that cryptocurrencies are accused of exhibiting today. Yet, they eventually wound up conquering the global financial landscape. They got their start by being convertible into the prevailing forms of money (gold & silver), just as BTC relies on convertibility into USD now. None of which is to say that BTC will necessarily be the next Big Thing in the world of currencies, but just that the ideas in the world of money which are widely held to be ridiculous today could very well be commonplace in 4 or 5 decades.