Do you really want the government of the United States to make it okay to kill American citizens it deems as terrorists, especially without a Declaration of War (which we did have in WW2)? Do you support the 2nd Amendment? Some Democrats have called the NRA a terrorist organization. Do you go to Church? Some on the left call Christians right wing terrorists.
Do you see the abuse waiting to happen?
I have no love for any American who joins Al-Qaeda. I hope they meet their Maker soon courtesy of the U.S. military. But this policy makes the President the judge, jury, and executioner of American citizens and we don't operate that way.
The authorization by Congress to use all necessary military force constitutes the functional equivalent of a formal Declaration of War.
The USA has formally declared war a grand total of 5 times under the Constitution, 4 of those after hostilities had started.
We have engaged in military action literally hundreds of times, with tacit or explicit congressional approval in most of those cases. The very first example was the Quasi-War with France, where President Adams fought without a formal declaration of war. This allowed both sides to pretend they weren't really at war.
As far as using military force against American citizens without a Declaration of War, this goes all the way back to Washington and the Whiskey Rebellion.
As I've said elsewhere, the traditional idea of a formally declared war is that it can be declared only against another nation-state. We need to either expand the concept and formally declare war on al-Quaeda, which would be fine by me, or recognize that in a time when our most aggressive enemies aren't nation-states, Declarations of War are obsolete.
Do I trust Obama to use such powers wisely? Hell, no! But that doesn't mean the powers are wrong, only that we elected a bad user twice.