I'm going to have to go with foreign policy since it's currently the issue effectively destroying the most lives.
Only if you assume that abortion is murder, which you have done, successfully proving my point in that other thread.
"Destroying lives" is accurate for abortion no matter where you fall on the "abortion is/is not murder" continuum. It is by definition destroying life.
To be semantic about it, one of the essential aspects of life is being able to survive on own abilities. In any case, the counter that banning abortions destroys lives can also be made (though here "destroy" is being used in a different way). Hey, people destroy their lives arguing for and against abortion.
To be sure, I couldn't care less. Abortion is pretty much the lowest on my list of political priorities.
As for the question at hand:
1. Corruption
2. Education
3. The Economy
4. National Debt
5. Foreign Policy
