The friendly fire is enabled for both teams because:
"for reds" cellwars, warday, or whatever that needs FF to be enabled.
"for blues" Killing freekillers, killing an abusive warden.
If the warden just keeps freekilling each round and enables FF and he is immune to it, people who want to try and stop him can't hurt him, and they can't defend them selves, since they will be killed by him.
As well as he can abuse it even harder by telling all reds to go to a cell, enable friendly fire and disabling it for a second to kill all of his team, and then freekills the reds in the cell.
Thus, immunity for friendly fire for the warden alone OR disabling friendly fire for blues only, isn't a good idea.
However if it's possible there could be an "All-damage from blues to blues" resistance for around 70%~95% for all blues, or for the warden only, that might be a better way to deal with things.
at least that's my point of view so far.
Thanks for the suggestion.