I am almost indifferent to the foreign policy side of the constitutional problems, they pale in comparison to indefinite detention of you or me without due process, NSA letters that you aren't allowed to even discuss with your attorney, VIPER teams setting up paper check roadblocks inside the U.S. I don't really have a problem with drone strikes against terrorist targets either. Letting the C.I.A. get away with torture is pretty disturbing.
I don't give a shit about the life of a terrorist. But, look at the NSA, as you point out. It was a baby step for them to go from tapping suspected terrorists to tapping US citizens on US soil. I don't think its a huge leap from killing US citizens (or others) in a non-war zone with no warrant and no trial, to applying that domestically. Let's imagine that here, say in Texas, where the death penalty is liberally applied. Maybe some hypothetical governor of Texas could decide that he's reasonably sure that John Smith raped and killed that poor little kid in Amarillo, and his advisers have intelligence to that effect. Therefore, he decides that instead of capture that the whole community would be better off if they just went ahead and took out his house (as I'm writing this its occurring to me that this is exactly what happened with the Branch Davidians, except sub Gov for Atty General). Now imagine that with drones. Sounds far fetched, but if you give them an inch...