What about suffering which is not caused by humans ? For example, consider earthquakes, floods, volcano eruptions, asteroid impacts, plague outbreaks, and the like. To use a lighter example, do we really need as many cases of the common cold as we are currently experiencing all over the world ?
The common answer to this question is something along the lines of "God moves in mysterious ways" -- which does make sense once you posit such a God -- but you said that "the optimal amount of suffering is a good deal less than we see", so perhaps you have a different answer ?
I think that suffering that is limited only to what humans cannot prevent would be the optimal amount. This is because it is the amount that would exist in the optimal universe, i.e. where each individual human strives to be maximally good.
As for cases of the common cold, a lot of those are preventable; given proper medical research and distribution of medicines. Since they are preventable, I think that they should be prevented.
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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.
Welcome to Less Wrong, and we look forward to hearing from you throughout the site!
Note from orthonormal: MBlume and other contributors wrote the original version of this welcome post, and I've edited it a fair bit. If there's anything I should add or update on this post (especially broken links), please send me a private message—I may not notice a comment on the post. Finally, once this gets past 500 comments, anyone is welcome to copy and edit this intro to start the next welcome thread.