After the crash, dreams die hard for Wall Street crypto bankers. : Squeamish from the start about pursuing profits in one of the darker corners of finance, established firms this year slowed their already halting efforts to make a business out of Bitcoin mania. While none has thrown in the towel, and some continue to develop a trading infrastructure, most flinched as the value of virtual coins collapsed. Take Goldman Sachs Group Inc., which sought to position itself at the cutting edge of digital assets that skeptics see mainly as a domain of day traders and anarchists.