I'd disagree and say that animals do in fact "talk" or convey meaning. I have raised multiple dogs and with time your understand their needs: I want to eat, I want to play, I want to show you something (or alert you of something). These are the three things that most dogs will learn to convey to you.

We consider that animals are of a lesser species so that we can take advantage of them without any "legal or moral" consequences. Like we eat animals on a regular basis. We do deadly trial medicines on them. We raise animals against their will (like birds) and cage them.

Obligatory SMBC: http://www.smbc-comics.com/index.php?id=3864