Most of you are missing the point of carrying dogs in the trailer. It's not just sick or tired dogs being carried. And the trailer is the least dangerous place to carry dogs. 
They often carry totally healthy dogs in the trailer when they don't need full power on easy trail. So they can rotate all the dogs into the resting mode.
They also carry dogs to reduce the power of the team for better control on bad trail. Put their strongest two in the trailer and they can slow down the rest more easily.  
The dogs are less safe in the forward part of the sled which takes the brunt of collisions.  
And they will have more collisions and roll-overs if they haul dogs in the front of the sled since it puts too much weight in front and greatly reduces the ability to steer.
I think the Board's concern is exactly what they said...the inability of the musher to constantly see the carried dogs behind them. But the benefits of carrying them in the trailer out weighs the risk.