The best reason to brand someone with a pejorative label is to push them away, to forestall useful conversation, to turn them into the other.
Much more useful: Identify the behavior that's counter-productive. When we talk about the behavior, we have a chance to make change happen.
What would happen if the behavior stopped?
When we call someone misogynist or racist or sexist or a capitalist, a socialist or an abstract expressionist, what are we hoping for? Every one of us is on the 'ist' spectrum, so the label becomes meaningless. Meaningless labels are noise, noise that lasts.
If that person stopped acting like a _____ist, what would change? Because if there's nothing we want to change, the labeling is useless. And if there's a change that needs to be made, let's talk about what it is.