Without a shared objective standard (or even belief that one exists), there is nothing to appeal to and therefore no way to rationally persuade someone who disagrees with you.
Writing about LGBT activists’ recent campaign against a church, Nathanael Blake comments on why we’ve been seeing a decrease in tolerance and an increase in rage. The culprit, he says, is the subjective nature of gender identity claims coupled with our culture’s relativism—a relativism that makes it impossible to adjudicate rationally between two competing claims.
[M]oral disagreements over claims of transgender identity appear intractable, which is why, upon learning of a sermon with which they disagreed, local LGBT activists and their allies responded by trying to coerce and shame the pastor and his church, rather than by attempting to demonstrate why he was wrong. These activists sought not to persuade but to purge.
This is in large part because our culture lacks a common philosophy or theology that these activists can appeal to in making their case, and many would explicitly disavow the possibility of any such standard of truth or goodness. But this acceptance of moral relativism does not make our sense of moral imperatives disappear or seen less urgent. Rather, it has made moral arguments more emotive and irreconcilable.
Differing moral viewpoints seem as arbitrary and irreconcilable as sports fandoms, where we support teams based on locality, ancestral loyalties, or personal whimsy. Thus, when emotional appeals or demonstrations fail, pressure replaces persuasion, and shunning takes the place of reasoning. [Emphasis added.]