Huh, I remember this story. Anyway....
This story strikes me as a tad oversimplified. Claiming that the total sum of all good and bad events are indeterminable. From the uncertain future, anything is possible. So any future event may make use of past misfortunes. The underlining problem in this parable is time, and all good and bad are "ends" rather than "means." I won't argue if all good or bad things aren't means, rather not all are ends.
If time was indefinite, as infinite into the future and past, all final ends are void. But what action should anyone take? If nothing is good, or bad, all action is bias. Example, the farmer helped his son, when he could have choose not too. The son could have died, and there will be one less mouth to feed. Instead the farmer help his son's suffering. Promoting happiness over pain. The farmer "had" to choose an action in life. While this view is subjective, there is always one outcome that is usually the better, or best. The son help's the fathers uncertain future, and had a obligation to family. Evil doers actions tend to destroy more than create, or promote happiness. Villains may think there actions are good, but that just makes them more wrong.
Overall the parable is good. It gives a big question argument to them religious/moral/knowledge big universal concepts. I had to sit back and think over this review for about twenty minutes before coming to a conclusion.