The sin of humankind

It is very hurtful to see my tortoise fell sick. He refuses to eat and several times splutters liquid from his mouth. His condition currently is stable, probably due to the good nutrition he has received all these time. However, as the caregiver of the tortoise, I cannot refrain blaming myself for his illness. I kept looking back at where I have neglected him, exposed him to unsuitable environment (temperature, humidity), failed to provide balanced nutrition and health check-ups. After being despondent for a while, I start to blame other parties, such as the person who gave him to me due to inability to keep him as a pet, and then to hunters who first took him from the forest and sell him as a pet. It's really awful what human have done to the innocent animals. We took them from their natural habitat but, regardless of all the effort to understand their metabolism and behavior, we still fail to give them the appropriate nurture. And yet we treat them as the lowest citizen without paying much respect to their lives. If they die, we just say, "Well, it's only animal." I don't know how big our sins have become. I guess animals also have the same position in the eyes of God and human can only prentend to be of a higher degree by lowering other species.