Maybe a major issue with politics in the current western view, is not that it is identity-based but that it is a large atomic decision. You either get everything from the Repuplicans/Conservatives/Right-wingish or everything from the Democrats/Labour/Socialist/Left-wingish.
It is much easier to identity as broadly one wing or the other, so I will tend to vote one way even if some of my party's policies are terrible and some of the oppositions are great.
Well put. And there are so many issues that it takes a lot of effort to even understand them all. So often you just say, well I care about / identify with my party on issues a, b, c so I vote for them. Issues x, y, z that I know little about I will support the party line because if my group says that is the way to go then that is the way to go.
It is much easier to identity as broadly one wing or the other, so I will tend to vote one way even if some of my party's policies are terrible and some of the oppositions are great.