I think if you evacuated and could justify the call, then you would be acting within your obligations.
But if you evacuated when the situation was otherwise under control, and someone was injured as a result, then I think you would be hardpressed to say that evacuation was the best thing to do.
As for stating which side to evacuate?
As commander, I feel it is still your obligation to do as much in your power to ensure that even if an evacuation is called for, that passengers are as protected as possible.
By leaving it open to interpretation by the cabin crew as to which side to jump from would seem to me to be a bit of a cheap effort. Surely it's a team effort until you have finished the post disaster pint, and head home.