To be fair to Polyphemus, if a bunch of strangers broke into my home and killed and ate my pet(s), I would probably try to kill all of them too. I wouldn't care how hungry they were at that point. If you had waited five minutes for me to get home I would have made you some sandwiches, but NoOoOo.
Haven't seem anyone mention this yet, but in addition to Polities' words, it is deeply tragic that the first time being kind/making peace works, the Circe Saga, it's immediately followed by the saga where Odysseus decides to become a monster. Polites' kindness was proven to work, but everything else was just too much.