I started thinking about this question while I was reading the excellent book Ishmael recently. It’s a trickier question than it sounds. Here’s a thought experiment to show my thinking.
Let’s say I’m in a room with Charles Manson, who is 83 years old. Charlie is a mass murderer who is absolutely unrepentant for his crimes and would kill again in a second if he is let loose. His first victim would be me. By the way, Charlie has stage IV brain cancer and will die in a month. He doesn’t want to die, but he will.
Next to Charlie in a small soft pillowy bed is a 6 month old golden labrador retriever named Hero. Hero is in his prime of life. He belongs to a family who loves him. The family’s daughter is dying of cancer, and Hero sleeps with her every night. The family will be watching the whole experiment unfold together.
A soldier walks in with a rifle. I must choose in 15 seconds who will die: the beloved dog or the evil human? If neither, then the soldier will let Charlie loose and I die a painful death at his hands.
Whom do I kill? Whom would you kill? I’m leaning toward killing Charlie. It seems like one month of his life is worth less than the remaining years of Hero. He is so beloved and Charlie is such a cad.
Now try swapping out things. If you are inclined to save the dog here, then what if Hero had just never saved anyone and was just a dog from the pound? Or if Hero had been a sewer rat instead? 
Or what if it was your brother instead of Charle’s Manson?
At some point, making Charlie nicer or the animal meaner changes one’s perspective. Or, so I think, it should.
But perhaps you think Charlie wins still because humans are always more valuable than animals. If so, I think you are displaying what I think of as one of the most problematic memes of our culture: namely, that human lives are always more important than any other consideration. Even questions of whether to kill animals must always be framed in terms of their value to us humans.
Now, I’m not advocating for dehumanizing people here, or saying we should treat lizards like our brothers. But I am advocating for including these living beings in our moral calculus. For expanding our moral awareness. We should start talking about our animal brothers and sisters like they matter to us.
To stop systematically killing them in factories would be a good start… I’m not a vegan but I do feel horrible at how we treat animals as a culture and my part in it does bother me. Perhaps I will examine this in another post. This is a place where I’m evolving and learning personally.
