In the sixteenth century, amid Europe's religious wars, Sebastian Castellio formulated an idea that remains uncomfortably current: to kill a man is not to defend a doctrine; it is to kill a man.
The phrase arose in his criticism of religious persecution after the execution of Michael Servetus in Geneva. What matters is not only the historical episode. It is the distinction it raises: a cause, however important it may seem to us, does not automatically transform into moral everything we do to defend it.
Most of our current disputes are, of course, far from that extreme violence. But the mechanism can appear in miniature. Insulting someone does not strengthen an argument. Humiliating them does not make an idea truer. Turning a person into a caricature may give us the feeling of having defended our cause while, at the same time, impoverishing the way we are defending it.
This does not call for passivity. There are ideas that deserve firm opposition and conduct that must have consequences. Tolerating a person does not mean tolerating anything they do. The question is whether we are able to fight a conduct or an idea without forgetting that there is still a person in front of us.
There a difficulty appears that is not solved with good feelings: holding firmness without cruelty. Defending convictions without turning them into permission to despise. Setting limits without needing to deny the other's humanity.
Castellio was writing about a stake. We almost always argue from far less dramatic places. For that very reason we should have room to do it better.