Just prior to my debate at Oxford Union I asked the organizers; had there ever been an unanimous vote on any debate? They replied; oh no, that would be a very bad result because it meant that they had formulated a very poor proposition to be debated and/or that they had formed very unbalanced debating teams for and against the proposition. In my case I suppose you could declare it a perfect debate because it ended in a tie.
The Oxford Student reported this about the debate (paraphrased): The case for the proposition was based on a political double standard as to how far the state could go with prohibition. The war on drugs created and gave power to drug dealers which causes crime and violence. The war on drugs is doomed to fail because the more it is advanced, the more money and power it provides organized crime. The case for the opposition was based largely on the idea that drugs are dangerous and are otherwise useless. The “war” has really never been tried and has been too liberal, not too punitive. They argued that we must use “tough love” and that legalization would lead to an immense population of hardened drug addicts, crime, and death. The verdict: The debate ended in a draw and Union President Ben Sullivan had a casting vote, which meant that the opposition won.