I love animals but they aren't legally the same as people. If somebody sold a person, or controlled who they could have children with, we would be horrified, but we accept those as normal for pets because we don't treat them the same as people.
We put beloved pets to sleep if they're really ill with no hope of cure because we are responsible for them, and cats, dogs etc have no way, by definition, of understanding the situation or communicating what they would want.
A person is categorically different. We don't hold the same power to even decide between life and death over people that we do over pets, and rightly so! The comparison with pets is flawed.