Yeh that lawful good character is now homicidal against friends but still somehow lawful good with the exact same personality because the DM who does not really know much about the beast decides that is their nature .. SHEESH this definitely screams the DM is a "not fit for gramma" (if you don't like the word adversarial there are worse)
Oh come on. No one is advocating this. The most I said was a saving throw t
o act for a single round against the party. As in you might take a single attack, make another saving throw, then stop. No one is saying that the PC automatically turns against the party every time and must always try to kill the other PC's. Talky about adversarial interpretations. Sheesh.
After all, it would also be pretty plausible that the polymorphed beast runs away as well. Most animals don't fight to the death. Taking a fair chunk of damage will usually result in an animal leaving. But, apparently it's entirely plausible to you that the polymorphed beast will ALWAYS fight to the death. Since we're talking about what's believable and all that.
But, in any case, wouldn't the simplest fix be to limit polymorph the same way that druids are? Your max CR=caster level/3. Poof, all these problems go away.
Good grief. Even the slightest whiff of actually having to role play something and people react like you're asking them to eat puppies.