The best part of the fediverse is that anyone can run their own server. The downside of this is that anyone can easily create hordes of fake accounts, as I will now demonstrate.
Fighting fake accounts is hard and most implementations do not currently have an effective way of filtering out fake accounts. I'm sure that the developers will step in if this becomes a bigger problem. Until then, remember that votes are just a number.
So far, the majority of content that approaches spam I've come across on Lemmy has been posts on [email protected] which highlight an issue attributed to the fediverse, but which ultimately have a corollary issue on centralised platforms.
Obviously there are challenges to address running any user-content hosting website, and since Lemmy is a comminity-driven project, it behooves the community to be aware of these challenges and actively resolve them.
But a lot of posts, intentionally or not, verge on the implication that the fediverse uniquely has the problem, which just feeds into the astroturfing of large, centralized media.