I have no problem provided that it is in character and the players can seperate in character actions from out of play. However, I would evaluate the circumstances carefully to see if there was a trend among certain players.
In the one campaign i was in, the party had tracked down a "demon" that had been stealing animals and killed a man. We found the "demon" , whom turned out to be a lion-person from another world posessing some advanced technology.
The party comprised of a halfling barbarian, a ranger, an archmage, a my monk and my rogue eventually tracked down the lion person. Upon tracking down the creature, the halfling, ranger and my rogue approached peacefuly to try to establish communication.
The lion-person would not let the rogue, ranger, and halfling approach to closely, but close enough that a conversation could take place. He told them that he stole the creatures for food and that he had killed the man in self defense. He would have asked for help from the beginning, but people reacted negatively. When the rogue, ranger and halfling offered to help him, the lion person allowed them to come closer. At five feet away, he asked them to drop their weapons and lie down. Sensing the lion man was trying to test our intentions and establish trust, we obliged, but only after telling the rest of the party not to attack.
Sure enough as the lion person knelt over our characters with his weapon drawn, the archmage attacked and the monk joined him. As the ranger stood there watching dumfounded (he was new to the party and had no idea whom to support). the halfling and my rogue tried to get in the middle and get both parties to stop firing. When the lion man fell to the ground, the halfling tried layed across him to shield the body. The archmage still kept firing away with spells even though the GM warned him that he might hit the halfling. Meanwhile, the Rogue was busy trying to keep the Monk from pulling the halfling from the lion man's .
The Lion man eventually died and the party was fragmented. The halfling and rogue wanted to nothing to do with the psychotic archmage (the player's character are always blood thirsty and power hungry, but the GM had always "tolerated" him) or the monk. The Rogue and the halfling buried the Lion Man. Then they left telling the archmage and monk not to follow, because it was taking all their restraint not to kill them on the spot. As for the Ranger, they accepted his explanation that he did not know the party that well and was ,therefore, unsure whose side to take and told him that he could along if he wished.
Eventually, the Ranger caught up to the Rogue and Halfling.
Now as for the GM, he was very upset with the player of the archmage and to a lesser extent the player of the monk. When told by myself that the player of the Halfling that our characters would never be willing to adventure with the Archmage again and would have to think hard before teaming up with the monk, the GM told the players of those characters that their characters were now NPCs. He felt that neither character had been heroic, and the archmage was downright evil. Given the choice he would rather DM the campaign using the Rogue and halfling.
After the game, the GM decided to kick the archmage's player out of the group, The DM had warned the player several times of his playing style. However the player of the Monk was allowed to stay (he just had to make up a new character)
The archmage ended up becoming the major enemy of the campaign and the the Monk was his top commander.
