It is no fault of our progressive society that, despite trying for political correctness and proper treatment of all humans, we still fall to the deeply objective treatment of any man or woman who does something—anything!—whatsoever. Is it because, deep down, we all harbor unsettling misanthropy? Or are we just lazy? Whether referring to ol' Brenda down the street, Uncle Charles, or even Steve, they are all human, and all deserve to be treated as such.
What am I getting at: equality, progressive ideals, liberalism, some form of humanism? Hell no. I'm getting at this: when referring to a person (no matter the stature), use who and whom, not that or which. Don't say The man that shot the rooster is bad, but The man who shot the rooster is bad. Same goes for women, kids, grandparents, and whoever identifies as human. And for anything else, use that. The fine lady, who was dressed in all black, wrote with a pen that stuck painfully to her fist.
Of course, there might be a few of you really progressive thinkers who are saying, what about my pig, Waddles? Well, that's where the debate starts, and I'm going to side with Mary Norris, from The New Yorker, on this. If you named a pig Waddles, then Waddles has every damn right to the who pronoun. Waddles, who some of you might know is fictional, is a pig. But if an animal is unnamed, don't personify it. That's where I stand on the issue, but if the buck doesn't stop there for you, here is one final option voiced by some animal lovers: Refer to animals that hold an important place in their own societal sphere with who—monkeys, wolves, orcas—and animals that are simply one of many—ants, birds, all cockroaches and all spiders—with that.
All humans use who; all named animals (or animals within a member-defined societal system) use who; and everything else uses that. Couldn't be simpler.