It seems to me that this essay takes a good starting point and stretches it thin. Your thesis can be put in a sentence: human concern for animal welfare is an ecological matter, involving not just particular organisms, but the welfare of all interconnected living things, including people. That's a premise, and the point of the essay ought not to be to prove it, or indeed to argue for it, but rather to show where it leads. Those who incline to dispute the premise may be interested, or even convinced by the consequences. But instead of developing the idea, to bring new and more adventurous ideas forth from it, you descend from it, and in the end wind up with a conclusion that could be put at two sentences distance from the thesis without loss of meaning. In revision, you should push the argument outward, away from the premise and towards new horizons, rather than towards the smallest objections you can find to vanquish.