A recent article, among others, in the Telegraph-News notes that Democrats are picking up on the Republican tactic of using wedge issues. But I think this comparison overlooks a key element in the way wedge issues have worked. Evolution, specifically the teaching of evolution in the schools, works as a wedge issue because an opinion one way or the other has no practical consequences for most people. The majority of students are memorizing one thing and/or the other for an exam, and then they are done with it, as virtually all adults are, for the rest of their lives. Their opinion, or what is done in the name it, is unhampered by any practical consequences for them. A few people may resent the degradation of learning and scholarship — science teachers have balked at the insult to their discipline — but for the most part it is of little or no concern.
Abortion is a more interesting example, because it has been of practical concern to young people and their families at least as long I've been around. But so long as the Republicans used a bait-and-switch of talking it up during the election and doing nothing about it once they were elected, it could function as wedge issue too. And, it is precisely this, the fact numerous state legislatures are passing laws that threaten to take us back to coat hangers, back alleys, and unexplained vacations that mean it is not a wedge issue anymore. It is becoming a real issue with practical consequences for more and more of the electorate.
Diagrammatically this brings out the necessity of there being practical consequences which can be assessed with regard to a concept or diagram. Otherwise, anything goes. And while we may still discuss the assumptions, applications, internal consistency, and even theoretical consequences of a concept, without practical consequences to the persons involved, all those things can be blithely ignored, distorted, and/or trivialized.