Imagine two universes where there is some idea for a big Jewish event. In Universe A, the original promoters of the event are on the Jewish left, in Universe B, they're on the right. In both cases, though, there is a desire for the event to be a "big tent" -- to include Jews of a wide range of backgrounds and ideologies.
- In Universe A, the event initially starts off as a creature of the Jewish left, and so the efforts to reach out and be inclusive mean reaching out to the Jewish right. Such outreach, I believe, would be interpreted by the Jewish left as diluting or tainting the message -- these "outreach" efforts would viewed as "sops" to the Jewish right, taking the event and making it more right-wing.
- In Universe B, the event initially starts off as a creature of the Jewish right, and the efforts to reach out and establish a big tent mean reaching out to the Jewish left (this was the story of the No Fear rally). Here, the Jewish left would view the genesis of the rally -- that it originated on the right -- as corrupting and suspect, they wouldn't want to participate in what they think is a right-wing stalking horse.
Do you see the paradox? If the supposed-to-be-united event begins as a left-wing event, efforts to expand the tent will be viewed as converting it into a right-wing event. And if the supposed-to-be-united event begins as a right-wing event, efforts to expand the tent will be viewed as laundering a right-wing event. Either way, the perception is that the supposed-to-be-united event is right-wing!
Now, perhaps part of the problem here is that a "united" event may end up over-representing the Jewish right as a purported sop to "unity", even though most Jews are not on the right. But even accounting for that, it is a problem when Jewish liberal groups feel as if "unity" events inherently are conservative events -- for many reasons, but one of the largest is that it discourages liberal Jews from showing up and taking their rightful place in the Jewish big tent, even though we very much belong there.
Something needs to be done to fix this, but I'm not sure what.
* This mean I'm not talking about left-wing Jewish groups that self-consciously hold themselves out as dissidents or gadflies, and intentionally separate themselves from such "united" gatherings. Whatever the merits or demerits of that approach, the groups I have in mind do not intend to adopt it.