3^^^3 people isn't "a very large number." The population of Earth or a galaxy full of inhabited planets would be a very large number. 3^^^3 is an incomprehensibly large number which is why it can lead to odd outcomes. If it were merely something like everyone on Earth suffering a dust speck then of course you choose dust.

Now, it's equally inconceivable that you would ever be able to affect the lives of 3^^^3 people so if you ever find yourself making a choice between 3^^^3 dust specks and torture you should choose dust because it isn't hard to imagine that your choices could result in a person being tortured. But that's different than the moral judgement in the abstract.