I can think of absolutely no reason why BMW did not provide a defeat switch for the auto dimming feature.
There are some driving conditions where I find that the dark mirrors make it difficult to see what is behind me such as when driving on crowded freeways after dark. There are some situations when I want to be able to reduce the glare from bright lights behind me and I want the mirrors to dim.
Drivers Club at Lime Rock
The Glen Club
International Motor Racing Research Center
Cayman Club Nor'Easters
Madison Ave. Sports Car Driving and Chowder Society (Only a Vice President)
Sports Car Club of America
Polish Racing Drivers of America (PRDA)
American Mural Project
Simeone Foundation Automotive Museum
Mount Washington Observatory
Society of Automotive Historians