I might have to to do that with mine too

suddenly realizes maybe they do it to increase friend count and karma.

You don't have to defriend them. You can opt no to follow them. It's assumed they friended you because they were interested in your plurks.

Or they were karmawhoring.

he had 110 friends after 2 weeks, so I guess it is the kwhoring. If I kept them I'd have 1 more friend but I'd be a kwhore, too

I don't friend people I don't know. Period.