For me there are a number of answers to your question:

- I love HN because I get to learn about lots of stuff I know very little about. For example I'm a business guy not a progammer, but I love to learn more about the non-business things. I genuinely can't judge the 'good or bad' on my own on some of this stuff. The karma gives me a quick and simple way of the community - this wonderful, intelligent community - pointing me in the right direction.

- It also shows where my comments might be off base - not because my comments karma is high or low (which I still see) but because I can see if the counter arguments are rated highly. For example I can't see if your comment is highly regarded or not. If was +40, compared to +1, I'd be more likely to think 'hmm, maybe I'm wrong on this after all'. Sometime is not just the power of the argument that changes minds, it's the weight behind it. I can't see that weight now.

-sometimes I quickly browse HN with some minutes of down time. Sometimes I read in depth. I now feel I'm being forced all the time to read in depth. Whilst that sounds good, in practise for me it isn't. Instead of more in depth reading I'm just cutting out the browsing, so I feel ultimately I'm getting less out of HN.

Other times, I don't have that much time and simply want to glean from the best comments on a post.

And then there are the posts in subject areas that are outside or on the edge of my expertise, where I have no business evaluating the comments. I can still benefit from reading them though, and the karma helps me give weight to the good ones and disregard the bad.