I thought so too, but about a year ago or so this same question popped up, and some of the comments were really eye opening.

The essence of it was something like this: if you use the upvote/downvote buttons as agree/disagree, then you’re contributing to turning this platform into an echo chamber, which is the particular thing that makes social media such a shitty place.

You should use this feature on posts to indicate if it’s relevant to the community’s rules or not, meets the community’s guidelines or not, contains factual, useful information or not.

On comments, you should use it to indicate if it’s relevant to the topic or not, valid argument to what they’re replying to or not, regardless of your own opinion.

A great example someone commented was, when he explained they were browsing lemmy together with his girlfriend, they had a great laugh at a comment, and then he promptly downvoted it, to her surprise. And it’s because, even though the comment was fantastic, it was off topic, it wasn’t useful for the actual conversation.

Oh, and actually, there was a thing, even on Reddit - believe it or not - which acted as upvote/downvote guidelines, describing how you should use those buttons.

I’ll try to link the original post here if I find it.

Edit: Here’s the comment I was referring to on the original post: https://lemmy.world/comment/5219066