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Reddit mods should be renamed spez's bitches.

I remember a similar case regarding Windows shipping with IE. Whatever happened with that?

Site policies can prevent that kind of behavior in that particular site. It's better than nothing.

I agree. One clear example is banning someone for participating on a community the mod doesn't like. Admins should learn from reddit's mistakes and limit what mods can and can't do.

But what’s the actual problem with the ability for posts to have negative scores?

It incentives self censorship that turns sites into echo chambers. e.g. Reddit

There's currently nothing stopping a mod from creating a bot to do the same. Maybe it's already a thing.

Do you have an example of a technology that is more efficient than human labor, doesn't have those side effects and was successfully held back just to keep jobs?

Here

I like being able to say what I want without being banned by a power-tripping mod

There's currently nothing stopping a mod from creating a bot that deletes comments below certain threshold or that bans users for commenting on communities they don't approve like they did on Reddit. Only site policies can prevent that.

I agree, but there already is a karma system.

Nobody cared at all

The mods cared. There were many bots used by moderators that relied on karma, the main one being automoderator.

It did if your karma was low enough. It also affected whether your votes were counted or not.