To get the most of Belmin's dialogue, the party has to approach him while an elf or half-elf is present as a party member. Belmin will verbally attack Jaheira and Aerie, expressing his disgust of the elven race. The latter two will listen to Belmin's tirade for awhile and then ignore him.
Should Viconia be present with the group, Belmin will assault her verbally for being a drow, declare that those all are evil abominations and then proceed to attack her. He is not dangerous at all and fights unarmed, but killing him in plain sight of the Amnish Guard standing just North of him will turn the guard hostile. However, should Viconia restrain herself from fighting back, the guard will attack and kill Gargas instead.