As a progressive myself, I have to agree with your assessment. Too many progressives, when they don't immediately get their way, either walk away from the Democratic Party and/or start tossing insults and aggrievement.

Coalitions are necessary and the "I won't take half a loaf because I want the whole loaf" is perfection undermining the good.

I do NOT see the progressives as akin to the Tea Party. Tea Party hung in there and moved the Republican Party to the right. They didn't depart the GOP.