back when reddit was not just a meme shithole, karma was used to motivate people to post quality content. 90% of the stuff posted on reddit nowadays would get downvoted into oblivion back then. typo in the title or image caption? downvoted. repost? downvoted. low effort? downvoted.
but with growing popularity the flat number of (usually young) users grew that hat other quality standards grew and these kind of faults were ignored. meme became bigger, and there was a general shift in reddits userbase. they changed the algorith to calculate your score and suddenly you could get just so.much.karma from cheap posts.
some communities became very strict in their content to avoid shitposts. some used karma to prevent trolls participating in their subs. nowadays high karma accounts are being sold as they can be used to participate in subreddits with a high reputation (due to participation limitations) and upvoting/downvoting and commenting on certain post can very heavily skew its visibility and impression of the discussed topic on “neutral” users.
so yea, karma used to be a good thing (good content motivation), became a bad thing (karmawhoring), which was still utilized for good things (participation limitation), which led to even worse things (karmafarming bots).
lemmy will have to deal with this sooner or later. there will be bots brigading communities on certain topics and there need to be some kind of indicators to distinguish honest users and trolls.
more importantly: different communites, different rules. If i want serious discussion on a topic, i can visit the community that enforces serious discussion. if i want some fun with it and see memes and shitpost comments to that topic, i go to the other community.
but i can not have a serious discussion post if it is enriched with memes from an other community.
i LOVE getting an overview of cross-posts. this allows me to learn about other communities, how active they are and how important or wide-spread a topic might be.