World-oriented consequences is all I can say about wanton killing.
Regarding talking to the known BBEG, are you relying on the BBEG getting to monologue? If so that's a bit much to ask of the players, how do they know this is not there only chance? Also what BBEG relies upn the PCs listening to his monologue? It sounds like he is totally unprepared for someone who might just jump him.
On getting "attack on sight players" to role play/care about information, use reasonable world-oriented situations, that is, most combat success comes through superior intelligence on the enemy, not bash door and swing. If all encounters can be overcome with charge and slash without thinking then they are too low a CR/EL.
Finally, where are the other players in this. When he says he's casting a spell you know someone could just interrupt him.
In the end, you probably have a play style difference. Talk to the other players see what they want.