The answer lies in the fact that we are unique. While we share many of the same biological processes as other mammals, we are the only species to have made any technological or cultural advancements whatsoever. We are also the only ones to question morality or existentialism. If we are indeed animals, then why should we care if what we do harms the earth? It is only by nature that we were inclined to do so in the first place.
The same argument is made on the basis of procreation and sexuality, which many will wave off as beyond their control because in the end humans are “no different” from the animals. From an evolutionary standpoint, we have absolutely nothing to gain from aiding the disabled or the elderly. In any animal society weakness simply isn't tolerated, and you would be left for dead if you found yourself in that position.
Our species is also unique in its ability to worship… anything. Wether you believe in god or you just devote yourself to mother earth, most people feel strongly about something, whereas animals are simply incapable of this higher level of thinking. Animals don't ask questions in any way shape or form. They are capable of understanding their surroundings, they are merely incapable of reflecting on them.
Despite the obvious advantages given to us by these traits, no other creature has developed anything similar. we are incapable of breeding outside of our own gene pool, and the missing link remains unfound.
Humans are only considered animals as a justification for evolution, which many don’t agree with.
Those who don't agree would be creationists, who believe that humans were specially made by God to rule over animals. Their theory is not without its own evidence. The mitochondria DNA of every living human is exactly the same, which is something passed down from your mother, who got it from her mother, no so on; suggesting we all come from the same ancestral mother, dubbed the mitochondrial Eve.
By turning back the clock on various ethnicities, we can conclude that modern humans have been around for 6,000 to 7,000 years, which coincides with the creationism. We also know that as early as 5,000 years ago humans have been smelting metal and getting tattoos as evidenced by the discovery of a frozen natural mummy called Ötzi. The point is that if we are not descended from animals, how can we be animals ourselves?
"Cheers"