What can familiars be?

It's only unethical if you treat the animal in question like you would a pure thoughtform familiar, IE: you use it as a shield.

I don't use Amelia as a shield. She merely helps me be freely providing energy. You may think it's strange, but, on an emotional level, an animal that bonds with you can be just as useful as any thoughtform. More so, especially when it comes to cats and certain larger birds, who are smarter then the rest of the animal kingdom.