The thing is, leftists dislike very much private property. As Bitcoin is the most absolute kind of private property ever invented, almost obsoleting the State to enforce it (which was not possible before), this can hardly be a left thing IMO. Don't forget that socialism feeds itself in the rogue capacity from the State to steal from the productive ones to give to its voters. Bitcoin will make it incredibly harder, so socialism could shrink as more and more people will opt out of the fiat system. Now they have a choice.