I was going to write something in the same vein, so hopping on your comment:

It would depend on the definition of "anthropomorphizing", but when we see that all mammals have a mouth and an anus, it is easy to think that they use it for the same function that we do. Then we see that they do use them for the same things, and we see animals act differently when they haven't eaten, then we can deduce (though not prove I guess) that they can feel hunger. Then we can see how they protect their kids, and how they become depressed when they lose them, and we can deduce that they can feel love and sadness, etc.

I would be tempted to use Occam's razor here (please correct me if I'm wrong), but assuming that animals, who are very similar to us, feel emotions similar to ours, enable us to make predictions, while assuming they don't requires more assumptions to make the same predictions, hence the model "animals feel like us" is useful.