simply untrue.
how can you play a yu gi oh duel without showing your deck?
-Player A sets a card
-Player B places a monster face-down
-Player A places a monster face-down because he doesn't want to show his card to the opponent
-player B does nothing because his deck is copyrighted
-player A doesn't activate his set card because he doesn't want to reveal his deck
[...] Turn 50, the game is still stalled
[...] Turn 500, both players die.