ehmm.. to long, did not read.. but to some of you: there's also difference between visibility of the action of playing the cards, and visibility what cards the opponents posess.. so both "Visibility of opponent's playing cards" as in "Deck of cards that can be played" and "Visibility of opponents playing cards" as in "Utilizing the cards they have in hand" are correct, but would mean different thing..

in other words:

you can play a game, where you only see opponent's card after he plays it,
or
you can play a game, where all the cards in his hand are visible

No, I thought you could see their cards when this setting is selected? If you go to the cards window there is a drop-down menu where you can select whose cards you want to see?

Nope, that is the "Visibility of opponent's cards" setting. The setting in question is the visibility of the opponent playing their cards and thus isn't possessive to my mind.