I'm surprised someone hasn't brought up the Australian Army Aviation multiple Blackhawk crash back in '96 on an SAS night training op. I think the official report stated that a demand by the customer to change the mission profile / route from the one practised in daylight was a major factor.
As someone said already, the aircraft captain, whatever his rank, simply has to have the balls to say 'no'. Not easy sometimes, particularly when the man you're saying no to might be writing your OER or have the ear of the man who will be writing it, but it has to be done.