You may be right that pilots won't suddenly leave. However Pilots may not join the bottom quite so quickly and transfers across from other airlines may well dry up. In addition morale will be shot to pieces and it won't be pleaseant to work for BA if the pension is nicked.
This Golden egg thing is rubbish - yes I am proud to work for BA and I am very lucky. However at the end of the day we are a company like anyone else. The arrogance that we are somehow the best is not true in many respects (although it is true in some).
The "Golden egg" will be somewhat tarnished if the pension goes, so see my first point.