I dont think he was shown as a joru ka gulaam. he was acting sensible.
The other person is down to violence with a gun. Now RK is neither a killer nor a goonda who doesnot mind if somebody gets killed.He observed that Sultan was actually listening to MB. So he thought may be the issue can be resolved with talking.The moment he realised that Sultan was again trying to harm them and was in no mood to listen he immediately started fighting himself.