Downvotes are already a questionable design choice, which encourage passive-aggressive drive-by behaviour rather than engaging with and countering challenging ideas. They’re kind of a dark feature, which give the user a sense of participation, or worse, the sense of being a cop, while contributing nothing.
They are catharsis without praxis, and they almost certainly contribute to online toxicity.
Actually giving them forum or site moderation power is… Well, it sure is doubling down on that feeling like a cop thing.
And what are all cops?
Because it abandoned the idea of the site admins being responsible for moderation, in the name of expanding to unmanagable size.
On Reddit and Facebook, groups do not have a common moderation team, so they lack the right to dump a post in someone else’s group.