Historical precedence is not an evidence for permissibility. That it is not a source of Islamic ruling should be clear – if taken to its conclusion that would mean that we can point to the actions of some of the leaders historically to align themselves with groups hostile to the Muslims such as the crusaders or Mongols, or enforced hereditary rule, or other indiscretions of specific rulers which went unchecked, whether personal or otherwise – and suggest that they were also permitted since they took place. Such an argument is irresponsible, incorrect and contrary to Islamic thought.