It is better to respond coolly to assholish behavior. But it is not better to allow it to remain unchallenged. Not challenging assholish behavior means that it becomes a community norm and is then incumbent upon everybody else to "train" themselves, as you say, to ignore the behavior of a minority of assholes. It hands the responsibility of defining what the culture is to those assholes.

Letting the assholes normalize the culture is bad. It decreases uptake. It increases, even if people "train" themselves, the likelihood of burnout and of departure. And it makes the world, even if incrementally, a worse place.