If the badness of specks add up when applied to a single person, then a single dust speck must have non-zero badness.
If I drink 10 liters of water in an hour, I will die from water intoxication, which is bad. But this doesn't mean that drinking water is always bad - on the contrary, I think we'll agree that drinking some water every once in a while is good.
Utility functions don't have to be linear - or even monotonic - over repeated actions.
With that said, I agree with your conclusion that a single dust speck has non-zero (in particular, positive) badness.
You know what? You are absolutely right.
If the background rate at which dust specks enter eyes is, say, once per day, then an additional dust speck is barely even noticeable. The 3^^^3 people probably wouldn't even be able to tell that they got an "extra" dust speck, even if they were keeping an excel spreadsheet and making entries every time they got a dust speck in their eye, and running relevant statistics on it. I think I just switched back to SPECKS. If a person can't be sure that something even happened to them, my utility function is rounding it off to zero.
Today's post, Torture vs. Dust Specks was originally published on 30 October 2007. A summary (taken from the LW wiki):
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