Karma is an inherently destructive thing for many reasons. For people, it is a representation of other people's approval of you, so they'll do anything to boost that number as highly as possible, even going so far as to make fake karma farming accounts, create botnets to upvote themselves and downvote opponents in arguments, and post garbage content instead of engaging in meaningful conversation with other people. For corporations, it's a marketing tool they can exploit to manipulate public opinion, by creating or buying high-karma accounts to convince people to buy shit, or to mass downvote people who point out flaws in their arguments or products, or figure out what they're planning and try to call them on it. They can use karma to discredit opponents, astroturf, and even sway elections indirectly. It's one of the reasons why civil and political discourse have completely collapsed in the USA.

That list is not exhaustive