I am trying to understand the reason why Leto III merged with the sandtrout in Children of Dune and why he was so committed to the Golden Path.

I just finished the first three books and I fear that I have missed the point of why prescience is so bad. According to the wikipedia entry, Leto wanted to teach humanity a lesson to avoid stagnation, so much so that he punishes them for 3,500 years by being a brutal emperor.

What isn't clear to me is how this actually saves humanity? Given the horrors of Muad'Dib's holy war and Leto's rule you'd think that having a few prescient noblepeople running around wouldn't be so bad. And why does he need to merge with a sandtrout and then let the Sandworms go extinct in order to accomplish this?

I checked out the Dune and Children of Dune miniseries in the hopes that the "made for TV" aspect would simplify the explanation of Leto's commitment but it doesn't do a good job explaining that either, it just seems to be a rehash of Leto's speeches on why the path is necessary.