"Why do we need anything to shoot at in the first place?"
Because of some of the alternatives.
1) Do nothing and wait for terrorism to wither away while we suffer an exhistance like Israel.
2) Wait to rebuild intellegence field opperations and then rely on police action
3) Continue the practice of lobbing Tommahawks into countries where we think the enemy might be
4) Become a closed society
For all the flap about collateral damage, if we are going to fight, it's far better to draw a bead than to drop bombs.