The karma system isn't enough for the purpose of learning; I fully agree to that. And to the point of this article, I usually don't downvote people, rather I try to correct them if I see something wrong. That, if anything, seems more appropriate to me. If I see an issue somewhere, it isn't enough to point it, I must be able to explain why it is an issue, and should propose a way to solve it.

But Eliezer has me swayed on that one. Now I'll downvote, even though I am, indeed, very uncertain of my own ability to correctly judge whether a post deserves to be downvoted or not. For that matter, I am very uncertain about the quality of my own contributions as well, so there too I can relate to your experience. Sometimes, I feel like I'm just digging myself deeper and deeper, that I am not up to the necessary quality required to post in here.

Now, if I was told what, in my writings, correlates with high karma, and what does, with low karma, I think I might be tempted to optimize my posting to karma - gathering, rather than adapting them to the purpose of making high quality, useful contributions.

That's a potential issue. Karma is correlated to quality and usefulness, but ultimately, other things than quality alone can come into play, and we don't want to elicit people's optimizing for those for their own sake alone (like, persuasiveness, rhetorics, seductive arguments, well written, soul sucking texts, etc.).

We really need to get beyond the karma system. But apparently none of the ways so far proposed would be workable, for lack of programming resources. We'll need to be vigilant till then.