To add to what other people said: As a casual user who didn't go deliberately looking for bots, I mostly caught them when they posted a comment that was a complete non sequitur to the comment they replied to, like they were posted in the wrong thread. Which, well, is because they were--they were copied from elsewhere in the comment section and randomly posted as a reply to a more prominent thread. Ctrl+F came in very handy there. (They do sometimes reword things, but generally only a couple of words, so searching for bits and pieces of their comment still usually turns up results.)
Also, the bot comments I caught were usually just a line or two, not entire paragraphs, even if they were copied from a longer comment.
There are very shy people like me who have to sit and work up their courage to post any comment, much less a dissenting one. (Edit: Or else yolo it and regret it later, like I kind of did with this one.) I'd have at least 4x (probably closer to 10x) the number of comments I have back on Reddit if I posted every comment I wrote and then ended up chickening out and not posting. And I've never commented on a heated thread where I disagreed with the popular opinion (or, at least, not about me disagreeing).
Anonymous upvotes and downvotes allow shy cowards like me to express our opinions in a small way without the fear of being attacked for them. Are they abused by assholes? Yes, but everything is. Assholes shit on everything, it's their way. Like I said in another comment, though I wouldn't be happy about it, I'd be willing to compromise by letting mods see voting history to prevent rampant abuse.
I don't want anybody knowing I, personally, disagree with X because I might be harassed for it, but I want people to know that somebody disagrees with it and they're not just in a big circlejerk. I said in another comment under this post that I used to be in a subreddit where I belatedly discovered a large number of people despised my favorite character and thought people who liked him were bad people because they liked him, or liked him because they were bad people, or something, I don't know. Either way, I certainly wasn't brave or stupid enough to go in there and argue, but being able to downvote the worst comments--before I realized how prevalent they were and left the sub--gave me some measure of agency there. I wouldn't be able to do the same thing here.
With anonymized voting, if you're careful to not say anything that gives away your location, they're not going to pinpoint where you are, beyond a broad area. With public voting, if you go to your town's magazine and upvote a bunch of stuff, they're going to know exactly where you are. That goes for anything else you might not want them or anyone else to know about you. They can certainly build a more complete psychological profile with both your comments and your voting history than with just your comments. And I know a lot of people don't care about privacy anymore, and I think that's a tragedy.