That is one heck of a good essay, and is almost something that might be delivered by a character talking about the creature.
I think one's viewpoint of a villain depends on age and villain in question. As I get older, I know horror does tend to scare me more, and therefore the villains tend to perhaps irritate me more. As an example, someone brought up the Governor from Walking Dead -- I really wanted to see his comeuppance because I know now, more so than when I was young, that there are people like that in real life who get away with doing what they want to do (and we as a society essentially allow it), and it is frustrating. And when you're younger, you think you know it all and will not be fooled by that type of thing...but then you realize you've been fooled all along, by everything. You realize you actually can't fight the world, you just have to stay away from it.
A villain like "It" is mostly different because of the degree of fantasy involved. Liking that villain and being fascinated by it is probably fine. In fact, I liked the It scenes the best myself. I will say this, though: taking your analysis and metaphor, maybe It is a jerk because it is no different in the way it feeds than we are when we send animals to the slaughterhouse -- there is horrible abuse at abattoirs, no matter what the stupid politicians who support farmer interests say, and while I have no problem eating meat, I want animals to be killed painlessly. I don't like bowhunting, I don't like steel traps, I don't like what humans do to chickens to get eggs and what they do to pigs; in that sense, is It like a crazier version of Ted Nugent? I would say It might be. It probably doesn't have to feed in the way it does.
If you take Hannibal Lecter, he is undeniably one of the most interesting villains out there. Yet, if I recall correctly, in one of the books he rationalizes his evil by saying, hey, God does worse, and he has done worse to me (what happened to his sister)...does he really care about his indiscretions? That is fascinating to contemplate, and I think it is quite allegorical, just as It may be allegorical of our distasteful way of producing meat -- if you think about it, no matter what humans say, life is cheap, people die every day, and no one seems to care, except to use the dead sometimes as martyrs.
So, as I get older, and I start to realize all this, the villains start to become scarier, especially based on how realistic they are. But I agree: when reading about them in books, they tend to be fascinating.
Again, that was a great essay you wrote...