A quick caveat: I am not talking about characters having disagreements or role-playing tensions between them. This post is specifically about using game mechanics to harm, hamper, or kill another character.
While obviously this is a social contract issue and is highly game and group dependent, I almost never allow it. Some games invite it - like Paranoia - but my experience has been that it is usually destructive, especially if the people at the table do not know each other well.
Additionally, while intra-party conflict is sometimes defended as just being role-playing ("it's what my character would do!") what I have witnessed is intra-party conflict is a tool that players who want to remove agency from other players use to accomplish their goals (i.e. bullying).
Again, this is group dependent, if this is not a problem you have ever experienced, then enjoy slaughtering each other. The one thing I might stop and ask though is: is everyone having fun?
The problem with intra-party conflict in my model above is that it can be initiated unilaterally. One character just takes a swipe at another and there is nothing that another player can do to stop it.
This is such a minefield of social variables that I find it simplest as the referee to just say no. The costs are small (characters cannot escalate a disagreement to physical force even if realistic). The benefits: no one walks away from my game feeling hurt, bullied, or otherwise upset.
Fortunately almost nobody reads my blog so it is unlikely that I will have to defend this position against the inevitable backlash this sort statement gets so I will leave you faithful readers with a few tenants of my games:
- No hurting other player characters. My game is not your forum to play out your bully fantasies.
- No stealing from other player characters. We are here to play together, I won't let you steal from another player's wallet and I won't let you steal from their character either.
- Only the player of a character may decide that character's actions, it is not your character so stop trying to tell them what to do.
- Decisions are not made by talking loudest or most.
- Play fair.
- Make sure everyone has a chance to participate.
- Make sure everyone is having fun.
Those tenants revolve around the ideas that one player may not take the agency of another player, and that the aim of the game is fun.