Coalitions are both the lifeblood and bane of the U.S. left. We have endless coalitions, but no Party, movements but no Movement. Coalitions facilitate a modicum of organizational unity at the cost of intellectual anarchy. My original post used the context of the Labor Party as an illustration of a problem.
My presumption is that when people consider a more-than- superficial commitment to a political party, they do not think only of short-term expediency, but, in enough cases to matter, think about whether the party reflects their vision for the future. Joining a party is not like joining the Price Club, if the party means anything.
So the problem of resolving cultural contradictions, even when the "left" is correct on issues such as choice, remains.