I don't think this is very humanitarian at all. I think animals have a certain way to communicating with one another and by devocalizing them, you would be taking a certain right that animals have to themselves and one another. This would be wrong on so many levels I don't even know where to begin.
Just as humans, animals have voices and they communicate with them. It would be abuse if a mother decided she did not want to hear her child cry so she has the child devocalized. When a person decides to become a pet owner, he or she is or should be aware that the animal may make noise, such as barking, meowing, whining or talking (birds). These things come along with being a pet owner. If this is not one of the things that a person can deal with, then they should find a more quiet animal like a fish.