I'm failing to understand why Garance is up in arms about Glenn Hurowitz being both involved in an anti-Hillary PAC and endorsing Edwards. If he's against Clinton, and he's a Democrat, I'd reckon he would be for someone ... and you've probably got a 50-50 shot on guessing who that person would be (if he's at all interested in efficacy ... I mean sure, he could go for Dodd or Kucinich, but that's doubtful). So his previous endorsement of Edwards doesn't really seem that newsworthy.
And Hurowitz is active in environmental circles, which is one area where Clinton's not enjoying as much support these days as both Edwards and Obama have come out with much more comprehensive, progressive climate and energy plans. It's plenty justifiable for groups and individuals to challenge Clinton's progressive credibility and work to counter what seems to be accepted gospel around these parts on her inevitability. Up until the primary, actual conversation and disagreements about the progressive merits of the candidates is a good thing, from what I gather. After that ... well, then Dems can fall in line behind the candidate.