Centaurs are among the creatures in the Harry Potter mythos that share a vastly different moral code than wizards and witches. This is also true of goblins to some degree. Centaurs make it a point not to involve themselves in the goings on of muggles or
wizardkind. That makes sense, given the kind of shenanigans people get up to. Bane, alpha of the Forbidden Forest centaur herd, is especially vocal in his belief that centaurs are well above two-legged types like us. When Firenze carries a young Harry on his back, he’s scolded by the herd for debasing himself like a common mule.
Eventually, Firenze is banished from his herd. We don’t read the scene directly, but Rowling does tell us that the aftermath of the centaur battle left Professor Firenze with deep purple hoofmarks on his chest. In fact, the centaurs might have actually killed Firenze if Hagrid had not intervened. It might have been cool to see a centaur battle, but we don’t think any fans would want to see anyone beating up on Firenze.