The virgin in the volcano example is also very helpful to u…

The virgin in the volcano example is also very helpful to understand another major problem with "the greater good" and "the end justifies the means":
You don't even know the "end".
If you murder the virgin for the "greater good" but then somehow rain doesn't come as a result of that, you now didn't even achieve any "greater good", but still did an evil thing.
The end that was supposed to justify the means never came.
The "greater good" that was supposed to justify the evil never manifested and now all you did was great evil.