Is it so hard to listen to my advice and make three civilian classes?One would be protective,one assaulting,and one neutral.
People who want to chill would go to neutral class.The assaulters and defenders would do their role like security/terrorists.As simple as that.They'd undergo balancing normally.And neutrals would be disarmed and immune to damage from other players.
So,they wouldn't be able to gang up and wreck a certain side anymore.