I come off as having double-standards
You come off as having single-standards. That is, I think the minimal level of niceness you accept from others is also the minimal level of niceness you practice - you don't allow wiggle room for others having different standards. I sincerely don't resent that! My model of nice people in general suggests y'all practice Postel's law ("Be liberal in what you accept and conservative in what you send"), but I don't think it's even consistent to demand that someone follow it.
extremely rude behavior (ie "I wish you were dead" or "X is crap.")
...I'm never going to live that one down, am I? Let's just say that there's an enormous amount of behaviours that I'd describe as "slightly blunter than politeness would allow, for the sake of clarity" and you'd describe as "extremely rude".
Also, while I've accepted the verdict that " is crap" is extremely rude and I shouldn't ever say it, I was taken aback at your assertion that it doesn't contribute anything. Surely "Don't use this thing for this purpose" is non-empty. By the same token, I'd actually be pretty okay with being told "I wish you were dead" in many contexts. For example, in a discussion of eugenics, I'd be quite fine with a position that implies I should be dead, and would much rather hear it than have others dance around the implication.
Maybe the lesson for you is that many people suck really bad at phrasing things, so you should apply the principle of charity harder and be tolerant if they can't be both as nice and as clear as you'd have been and choose to sacrifice niceness? The lesson I've learned is that I should be more polite in general, more polite to you in particular, look harder for nice phrasings, and spell out implications rather than try to bake them in connotations.
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A list of some posts that are pretty awesome
I recommend the major sequences to everybody, but I realize how daunting they look at first. So for purposes of immediate gratification, the following posts are particularly interesting/illuminating/provocative and don't require any previous reading:
More suggestions are welcome! Or just check out the top-rated posts from the history of Less Wrong. Most posts at +50 or more are well worth your time.
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