It appears that a debate on roll cages has emerged on various forums. I will always enforce the cage rule for tandem at my events. There are some venues that allow cages and I actually think it is fine at those tracks for now because:
The tracks in Southern California that are allowing tandem are slow tracks with plenty run off areas. This means if the lead cars spins out or goes off the track, the driver leading and driver following has time to react and avoid a collision. In the case of tracks like NOS or Irwindale, if the lead car spins or unders, he has a split second to correct or he goes into the wall. When there is a wall, you have no escape zone or run off areas. You are stationary on the track and guess what, there is still another car right behind you that needs to avoid you some how.
So in the case of a collision on a track with walls, there needs to be safety equipment in place to protect the lead and chase car..... Bottom line.