Do you think the good/bad feelings people get from an upvote/downvote are more relative to other people's karma [...], or do you think they're more independent of other people's karma?
I have no one's experience to go on but my own, but here was mine: when I first started commenting on LW, I was nervous and afraid of downvotes and I didn't care at all about other people's karma; I just wanted to not look terribly stupid. Now that I have been here for a long time and made probably many more comments than I should have (for my health), the main things that bother me are when a downvote is unexpected or when I make a comment and a reply is contradicting me and that reply has more karma than the comment I made. And other times when my comments seem to me to be just as good as other comments in the thread, but get nowhere near as much karma. And also, I'm not entirely sure if we want to encourage the type of person who is hypersensitive to downvotes to come here. My gut says we do, but it also says we relax our desire to not have bad comments too much relative to this type of person's actual value. Complex question.
In particular, Harry Potter comments
I know! If total karma were hidden, though, it wouldn't as much of a problem. People could just weight against the inflation in 'fun' threads like that. (Ever notice how fun-type threads inflate karma?) I also agree with you that posts in Main should have 3x karma instead of 10x. (I was pretty shocked when I found out it was 10x after writing this; if it had gotten the same score (though it wouldn't have)...)
Two points where I disagree with you on what to downvote are very short comments
This is one place where you and I just seem to have different preferences. Maybe it's because you have an easier time understanding dense material, but I seem to require more words. As an unfair analogy, compare reading the Twelve Virtues of Rationality to the entire Sequences. Many lessons from the latter are in the former, but it's really hard to get them out of the former without the latter. I made a modest effort at this and actually surprised myself at how much I got right, but most people do not do this.
and what you call "signals of pseudo-modesty"
I have since changed my opinion of this slightly; since underconfidence is a rare enough sin I usually respond to it with a private message with inquiry rather than a downvote (note also that I mentioned this in the context of thinking a comment is looking for karma; I acknowledge how low the base rate is on this[!]).
Edit: Generally, karma has gotten massively inflated lately. Looking at both Top Comments sections, nearly all of the first 600 are from the last five months.
As of right now, 9 out of the top 10 discussion comments for last week are in the Harry Potter threads.
What if self-deception helps us be happy? What if just running out and overcoming bias will make us—gasp!—unhappy? Surely, true wisdom would be second-order rationality, choosing when to be rational. That way you can decide which cognitive biases should govern you, to maximize your happiness.
Leaving the morality aside, I doubt such a lunatic dislocation in the mind could really happen.
Second-order rationality implies that at some point, you will think to yourself, "And now, I will irrationally believe that I will win the lottery, in order to make myself happy." But we do not have such direct control over our beliefs. You cannot make yourself believe the sky is green by an act of will. You might be able to believe you believed it—though I have just made that more difficult for you by pointing out the difference. (You're welcome!) You might even believe you were happy and self-deceived; but you would not in fact be happy and self-deceived.
For second-order rationality to be genuinely rational, you would first need a good model of reality, to extrapolate the consequences of rationality and irrationality. If you then chose to be first-order irrational, you would need to forget this accurate view. And then forget the act of forgetting. I don't mean to commit the logical fallacy of generalizing from fictional evidence, but I think Orwell did a good job of extrapolating where this path leads.
You can't know the consequences of being biased, until you have already debiased yourself. And then it is too late for self-deception.
The other alternative is to choose blindly to remain biased, without any clear idea of the consequences. This is not second-order rationality. It is willful stupidity.
Be irrationally optimistic about your driving skills, and you will be happily unconcerned where others sweat and fear. You won't have to put up with the inconvenience of a seatbelt. You will be happily unconcerned for a day, a week, a year. Then CRASH, and spend the rest of your life wishing you could scratch the itch in your phantom limb. Or paralyzed from the neck down. Or dead. It's not inevitable, but it's possible; how probable is it? You can't make that tradeoff rationally unless you know your real driving skills, so you can figure out how much danger you're placing yourself in. You can't make that tradeoff rationally unless you know about biases like neglect of probability.
No matter how many days go by in blissful ignorance, it only takes a single mistake to undo a human life, to outweigh every penny you picked up from the railroad tracks of stupidity.
One of chief pieces of advice I give to aspiring rationalists is "Don't try to be clever." And, "Listen to those quiet, nagging doubts." If you don't know, you don't know what you don't know, you don't know how much you don't know, and you don't know how much you needed to know.
There is no second-order rationality. There is only a blind leap into what may or may not be a flaming lava pit. Once you know, it will be too late for blindness.
But people neglect this, because they do not know what they do not know. Unknown unknowns are not available. They do not focus on the blank area on the map, but treat it as if it corresponded to a blank territory. When they consider leaping blindly, they check their memory for dangers, and find no flaming lava pits in the blank map. Why not leap?
Been there. Tried that. Got burned. Don't try to be clever.
I once said to a friend that I suspected the happiness of stupidity was greatly overrated. And she shook her head seriously, and said, "No, it's not; it's really not."
Maybe there are stupid happy people out there. Maybe they are happier than you are. And life isn't fair, and you won't become happier by being jealous of what you can't have. I suspect the vast majority of Overcoming Bias readers could not achieve the "happiness of stupidity" if they tried. That way is closed to you. You can never achieve that degree of ignorance, you cannot forget what you know, you cannot unsee what you see.
The happiness of stupidity is closed to you. You will never have it short of actual brain damage, and maybe not even then. You should wonder, I think, whether the happiness of stupidity is optimal—if it is the most happiness that a human can aspire to—but it matters not. That way is closed to you, if it was ever open.
All that is left to you now, is to aspire to such happiness as a rationalist can achieve. I think it may prove greater, in the end. There are bounded paths and open-ended paths; plateaus on which to laze, and mountains to climb; and if climbing takes more effort, still the mountain rises higher in the end.
Also there is more to life than happiness; and other happinesses than your own may be at stake in your decisions.
But that is moot. By the time you realize you have a choice, there is no choice. You cannot unsee what you see. The other way is closed.