De-crowing is cruel and against the law in many places. Many vets will refuse to do such a procedure. De-barking a dog is also cruel and again illegal most places. Cropping dogs ears is banned in several places and is becoming unacceptable. It amazes me what people will do to animals and nature for their personal fulfillment.
Let a rooster crow as a rooster or don't own one.
Out of curiosity, what facts do you base your opinion this is cruel? Have you seen the birds after the procedure is done? What indication have you seen in them that they in pain or change their behavior in any other way?