Just to add a bit to Birah's comment:
WHy is there so much shmutz out there? Why is the world so filled with evil?
Why is avoiding it so difficult?
Why would Hashem create such a world?
For one simple reason: He loves Teshuvah, and is waiting for yours and mine every moment of every day.
Birah
The greater the opposition then the greater must be the force of good to withstand the forces of evil. Only in a world filled with evil, can a soul's heroic greatness shine forth. That's just my 2 cents anyway lol.
BW,
DL