Nothing is stopping a single individual from controlling 100 accounts on Lemmy to upvote and downvote whatever they want

I hate to break this to you, but there's only 43 people on lemmy at all. We're all just pretending to be everyone, including you.

You aren't you at all, you're a constructed personality inside someone's mind with a lifetime of false memories and a thin veneer of "free will" to give you the illusion of being a real person.