Yeah whenever we've had a meta-chat inevitably people come on and say "who cares about karma?"

That sounds all fine and dandy, but study after study has shown that if you put numbers/points/stars next to desired user behavior it is going to incentivize it. So yes, in theory it shouldn't matter at all, but due to the freaky way people's minds work, it actually matters a great deal.

It's not a logic thing.