Informative - I agree, but you may be full of shit

Interesting - I agree, stick it to those other guys

Funny - I agree, either schadenfreude or grits

Idealistically, humans would only vote based on content quality and not their personal opinions. But Slashdot is certainly the counter example on why this doesn't actually work

So "Insightful" as an "I agree, completely" on something that is not insightful may be metamoderated out.

It's basically impossible to do that if the value is only "+1".