Interesting topic for debate. I'm having a hard time deciding, but I know that Awlaki was plotting to do harm to American citizens while he lived in Yemen. And do you really think we could have captured and transported him back for trial in the U.S. without suffering casualties?
Of more consequence to me is the fact that the current administration considers people who believe like I do as likely (not just potential) terrorists.
In my estimation, the option to eliminate Americans overseas who have shown their efforts to harm the U.S. should require a judicial review, similar but more stringent than that required for wiretaps.