You underestimate universalism. It has adapted before. Recall that the Cathedral is a warm body machine, a belief pump. The victory of Democracy in the age of conscription and the printing press was no fluke. So as long as human minds by the billions can be thrown into the gears of war its complete defeat is unimaginable. What you must defend is not the ideology but the strategy. So clearly in order for this strategy to be viable you have to burn the mutant, kill the xeno and purge the heretics.

For the Emperor!