Stamping out the competition (going even as far as murder) is not necessarily irrational. Ruthlessness can be employed quite easily in a rational way. What might be irrational is them expecting everyone else to accept their actions and to not expect revulsion and reaction to their acts.
"Stamping out the competition is not necessarily irrational....ruthlessness can be employed quite easily in a rational way."Unfortunately too easy...Stalin,Pol Pot,Mao....