Revman - if you want the seat with extra legroom, PAY FOR IT.
If not, don't bleat!
In a prepared emergency, ABPs are going to be identified and moved. In an unprepared emergency, the average punter will panic and forget the briefing they got at the start of the flight. The net result being much the same as if no one was sitting in the exit row in the first place.
If it were such a critical issue, the regulators would mandate that a paid, trained person be adjacent to every exit, not just the door exits.
Just recall that the evacuation criteria at the certification level are based on the use of HALF the available exits anyway.