The problem isn't killing Al-Awliki, really. The problem is doing it the way it was done - publically, as a matter of national policy, in violation of international agreements and the US Constitution and Bill of Rights.

That's why there are Special Forces, folks who are supposed to operate in the dark, with deniability.

What this killing has done is tell the ROW in public that the US cannot be trusted. Can't be trusted to honor international agreements, can't even be trusted to respect it's own Constitution. And as the economic power of the US wanes, other countries will be free to regard us as just another rogue nation. If one doesn't respect oneself, no one else will either.

Operations such as this cost the perp more than the victim.