Not everything has to have a God vs. Satan based answer. Bad things happen because humans have the freedom of choice. There are biological and chemical factors that affect the way we think or rationalize things. Some people are just inherently evil, while others are mentally imbalanced. Far too often society wants to point the finger at a cause, place the blame, and speculate how and why something could happen. There's no need for a supernatural scapegoat. Look in the mirror and you'll see the reason why things happen. To think that God or some form of evil has influence on every decision and aspect of life is drivel. Talk about EXTREME micro-management. Do you really think God cares which shoes you decide to wear today? He's got bigger things to worry about.
Having said that, could God cause natural disasters to root out evil in certain places? Sure!
Could some people be possessed by evil and carry out a tragedy? Absolutely!
However, even Satan had to have God's permission before he could do anything toward Job and his family. So, based off that, the choice comes down to these options:
1. God allows/causes bad things to happen, which doesn't project the image of a very loving God.
2. Humans have free will and the freedom of choice, and bad things happen because of a choice that is made.
My belief is in #2. God is saddened by those choices and grieves for the innocents, but knows that the righteous will be called up to Heaven, and the wicked will be judged and cast into the lake of fire. I said this in another thread.
If God controls everything and we do not have free will, then what good is the judgment that Revelation speaks of when the dead are raised, because God would be judging Himself and what He allowed to happen.