I don't know, maybe that is true here but I've met a significant number of people who seem to think it is an actual thing.

I've heard arguments such as "I know god exists because karma exists" which just seems like nonsense to me.

I think that's more on sites like Reddit where the "karma" relates to the number of upvotes you have.

General use of karma is basically saying "what goes around, comes around". It's a derivative of the concept from dharmic religions.

Plenty of people literally believe in Karma.

Also, on the other side, your reputation of being an asshole can get around pretty quickly.