Here are my thoughts:
If you think about it, pulling the .ever would be the greater good, at least that's what we think.
1. If we can commit murder to cause a greater good, makes us no more ethical than a villian in a movie. If the villain seriously knew that it would end up for the better, he would still be the bad guy.
2. We don't know if it even is for the greater good, if the slightest change in the wind could cause a world changing event then we have absolutely no idea if it even is for the greater good.
3. We don't have the right to play mastermind with human lives. Even if we KNOW that we would end up with more human lives we still have no right to treat our own kind as a currency. If someone doesn't pull the lever, they don't commit murder. If they do pull the lever, they do commit murder, even if it's understandable.