Because, if we do not collectively exclude those who consistently disrespect moral law, they will undermine and ultimately destroy society from within.
In hindsight, it turns out that irrational numbers got a bad rap. They are actually quite useful, and they haven’t led to the erosion of mathematics from within, as, I guess, tragically, Pythagoras was so concerned about. In human society everything depends on adherence to rules and standards. Both music and morality can only survive if the collectivity has the means and ultimately the will to exclude rule-breakers.