All you have to do is have 2 separate playlists, one for single players to go into and one for only fireteams. I can understand that people will say "don't go in on your own then" or "go in with a fireteam". Not everyone has friends who play crucible or has fun playing a team of 4 stacks who just camps with healing rifts. I feel that every single players experience can be more enjoyable if bungie just had this simple mechanic in the game.