If Euthanasia is legal for animals why not humans?

This is a complex issue that touches on multiple concerns in a variety of fields.

Euthanasia of animals is legal for a number of reasons: animals are considered property under the law (equivalent to a TV or car); animals have not historically be afforded the same 'right to life' that humans have been; animals can result in significant financial burdens that are difficult to pass to a social safety net.

Deliberately causing the death of a human being, however, is considered to be a moral sin by most religious traditions (except in the case of self-defense or war). This argument is based on the concept that God gave all humans life so only God should be the one to take those lives away. Humans are also generally recognized as having a basic intrinsic 'right to life' that cannot be superceded by the wishes of another human being.

There are some groups that feel that humans should have the right to request assistance in ending their own lives; this is usually referred to as "assisted suicide", "physician-assisted suicide" or some variation thereof rather than euthanasia. The primary argument put forth by these groups is that humans have the right to decide what happens to their bodies while they are living but are contradictorially being denied the right to decide when they will exit that body.