If humans are animals, we are acting like animals, by definition.

What does it mean to "act like an animal"? Are we supposed to roam the plains of Africa eating plants, with a basic moral code, communally helping raise our young, like elephants? Or should we hunt in packs with a basic authoritarian hierarchy, like wolves? Perhaps we're supposed to be clever problem solvers like crows? Maybe we're supposed to befriend long-time acquaintances from other species, like lions, but otherwise eat lots of meat from those creatures we don't know?

It seems we do a good job acting like animals already.

But we aren't "just" animals (that's something you added, not us). We are animals - animals who have the intellectual capacity to write symphonies, and to take a step back and override our more primitive impulses.

We run into many people who are confused about "is" versus "ought". For instance, we recognize that Evolution is real, but that doesn't mean that we follow Evolution as some kind of philosophy. Evolution just is. Likewise, recognizing that humanity is a species of animal, doesn't suggest we ought to do anything.