It’s no surprise that Wences Casares, the CEO of Xapo, a bitcoin startup, is a big bull on the digital currency. His company, which specializes in insured Bitcoin vaults, just raised $20 million in a funding round led by Benchmark. But Mr. Casares belives that other bitcoin bulls, especially those in the U.S., do not fully appreciate the value of the currency, which has proved especially sticky in emerging markets prone to wild currency fluctuations, such as Mr. Casares’ home country Argentina. In a video interview with the Wall Street Journal, Mr. Casares says he’s not worried about bitcoin’s own...