what the Trots are not telling their multitudes--and you can see their fingerprints on so many of the "Left" opinions of the Greek case and the wild conspiracies centering on Tsipras--is that there was a leftist radical party that ran on the issue of leaving the EU ad Eurozone in the same election that brought Syriza to power. They got trounced.
Arby has it mostly right. The Greeks thought they could have their cake and eat it to, and they gambled on that and lost. Big. They genuinely believed the EU would do anything to prevent a departure, and so they had all the leverage. They had it completely backward. And if there's a "crime" that Syriza committed, it's that they, too, believed they had some leverage.
This resignation might do two things for the Greek left. I emphasize "might".
First, it might save the Left by taking responsibility for the situation and refusing to be scapegoated by a situation created by their corrupt predecessors.
Second, it might open up space for a more radical replacement that can finally reach the Greek people on the realities of European politics in the age of bank rule.
That's all there is left short of a violent descent into social unrest, which is pretty much what everyone outside of openly fascist players is trying to prevent.