An imperfect innovation like 1970s-era e-mail struggling to find its place in the market? Or “the mother and father of all scams,” benefiting insiders and costing naive investors their savings?

Members of the Senate Banking Committee struggled Thursday to balance the two contrasting assessments of cryptocurrencies like Bitcoin from witnesses testifying about the risks and the potential uses of forms of money that don’t exist outside of cyberspace and have no government backing.