It sort of gets into reducing the animals free will. It might not mind the paint but it also might not like it, and it can be hard to tell. There is also a good chance its toxic or causes some affect unintentionally.

Usually the thing I’ll ask, is who is benefiting from this action? If its not the animal, it probably shouldnt be done.

I think a good counter example is collars. My dog loves his collar because it means he’s going outside. It keeps him safe and others safe too. The collar is a good thing.