Idioma What animals can we kill and which cannot we kill?

I mean, if we kill animals like ants, no one (or almost of them) complains about it, but if we kill a dog, the world falls upon us. I'm not saying you have to kill dogs, in fact bastards who kill dogs deserve the same medicine, but why with other animals is not the same?
For example, if a fish is killed, there will be people who look it normal, not even complain about it. Why. Because they are not mammals? Nonetheless all they are living. Everyone. Dogs, locusts, ants, lizards, fish, birds, ...

From my point of view, it is possible to kill every mammal smaller than a cat (except pets like hamsters) without any problem.