Reddit Karma really just incentives unhelpful but funny/highly agreeable post. Upvotes are fine as a per-thread moderation system, but when you have a total of all up votes it opens the door to circlejerks and discriminating against users with low karma score (which also incentives circlejerks as a quick way to earn enough karma to be a valid user, enables paid shills and enables account selling).
Karma totals is more or less one of the biggest flaws with reddit.
Karma totals as an anti-spam mechanic are easily subvertable if you just get bots to upvote each others posts, and because it creates the appearance of a legitimate user it'll enviably create a account selling industry where spammers and corporate/political shills can just buy a "legitimate" accounts to just bypass karma restrictions.
Right now it might seem strange to buy a lemmy/fediverse account, but if the site ever gets big, then buying accounts would be a good investment for the wrong people.
In the end it just puts up a barrier for new users with an legitimate interest in sharing with the community.