R. Star wrote:
They still could've moved to a safe distance while the thing coasted to the asteroid field, then jumped back in with the tractor beam limiting their exposure.
But it would have fallen apart before it reached the asteroid field. The Enterprise
's shields were the only thing keeping it together long enough for it to coast on its own into the sun.
What difference would it make if the barge hit an asteriod, it appeared as if the asteriod field was far enough away from the planet that any raditaion resulting from the impact would have any impact on the planet.
This was really an environmental allegory about the safe disposal of dangerous chemicals. Sending the ship into the nearby sun was the best way to permanently get rid of the barge full of deadly waste without having it blown up and leave an irradiated zone in an inhabited system.