GCI35 and Peter, thank you for your explanations, as you can see pd2 you can probably tell that there are valid reasons for moving customers after they have boarded!
On my particular flight from Luxembourg, Mr "I know more than you" made his dissatisfaction known to all of us, for virtually the entire 50 minute flight! When I introduced him to the Captain on disembarking, explaining to the Captain that this was the Gentleman who was questioning his competency as a pilot (after all we were following his lawful commands), he suddenly turned from a captain of industry (that's what he told me anyway) into a red faced, bumbling school boy who couldn't get off the aircraft quick enough!
For reference, as well as the Rotterdam 737 incident. I seem to recall an Excalibur A 320 from LGW to MAN had a similar incident on take off back in 1992/3, due to incorrect loading ( yes I go back that far!). Am sure you ll be relieved pd2 that lessons are always learnt from incidences, hence the request to move seats! As a passenger on one of your flights, I wouldn't dream of questioning a lawful request that you or a colleague asked of me!