One other point that I think no one has mentioned yet is the importance of informed consent when treating people with otherwise fatal conditions. Surgery and other treatments e.g. chemotherapy for cancer incur a lot of pain and suffering in those going through it as well. A person can understand that all that suffering is for the greater good of extending their life, but for a pet that is far from the case, and they may in fact need to suffer more than if they weren’t treated.

I love my dog with my whole heart, but I would never put her through chemo if she had cancer.