It punishes the 2nd player to play the card. The 1st player gets the benefits of the Legendary, and the 2nd player doesn't even get the chance. All they can do is play it as a removal spell and then it's in the graveyard. That's really lame and takes away some cool stuff that would otherwise happen. The rule should have applied only to each controlling player. I don't see how this would have ruined the game or anything like that.