Yes (thinking of the final paragraph). But I'd take your description of the old Marxist left a step further and (as is often said in France of the old CP) point out that it had strong religious elements. They were belonging... and a certain kind of progressive teleology (one could fairly add eschatology with the inevitable demise of capitalism, the coming reign of the proletariat, etc). And I see the difficulty for us in precisely that element: what progressive teleology?

Otherwise, a quibble: religious groups do care about doctrine, immensely. Which doesn't detract from your other points about community, belonging, etc -- nor the point that rational criticism is unlikely to be persuasive.