Fenes said:
If I read "The arbiter doesn't feel the need to explain", I assume that the arbiter was not receptive to verbal questions. That, for me, rules diplomacy as a tool right out. Zone of truth and similar stuff also fails since there is no explanation to check.
And I vehemently disagree with a paladin being sworn to work within a system under all but evil tyrants - I say that his divine mandate takes precedence.
I agree that the diplomacy roll would be a DM judgment call. As a DM, if the player made a big argument/speech, I'd let him roll a diplomacy check to see if he nudges the arbiter from the "Hostile" setting. If there's a success, then, yeah, he starts talking to you.
But even if the DM doesn't rule that way, there's no way that I'd say that the player response would be described as inevitable, rather than horrifically played.
Why on earth didn't the paladin use his detect evil ability? (I assume he didn't use it on the mother, so we also have no idea if the MOTHER was evil, which was also a possibility. And kudos to her if she was. Good show!)
Why didn't the paladin use sense motive? That's a class skill for him, just as much as diplomacy.
Why didn't the paladin use knowledge: nobility and royalty to get a scrap of information about this guy? It's his one knowledge skill.
He also didn't use the campaign-specific options: talk to a religious superior, insist on taking this situation to court, have the sorcerer gather info on the Arbiter before he gets there, and he didn't press the case in the legal system.
He didn't ask the cleric at the birth of the children to cast Augury, Zone of Truth, or get divine guidance through other spells.
In short, he has no information that the child would even be in danger rather than unhappy and badly parented. And, however, much you disapprove, you don't kill a man for that. That's why the paladin has diplomacy and sense motive on his list. So, the "punish those who harm or threaten innocents" clause can't come into play.
And, for our purposes, we don't have to argue about the paladin's divine mandate and how it fits into secular society structures. 'Cause my basic point was that paladins are presumed to have some respect for the law, which this incident and his past history indicate a profound disrespect for divine and secular laws. (There's no way that bringing a sword to a fist fight that you and your buddies started respects a divine mandate.)
And I can't wait to hear how he explains to the little girl and little boy that he murdered their father, cut off his head, and burned his body. One would imagine that such a tale would be... emotionally scarring, to say the least. Especially since one of their first questions is going to be "Why did mommy not like daddy?" And his response is going to be, "You know what? I never bothered to find out."
Verdict: Not Lawful. Get a new paladin alternate class or get an atonement.