I take the keys too. I've done it many a time. Usually the Drinker(s) then would either walk or get a taxi to get more booze/go home. Both options are very reasonable in the small town I live in.
My concern is not usually the alcoholic, but myself. I do this at my home. I am responsible. I can be held legally responsible for allowing a drunk to drive, especially because I am usually not drinking at all.