Well.. here we have due process. Who and what determines the purported "violent actions" and the guilt of the accused? I don't pretend to know the methodologies as to how the Brit government concludes who's a legitimate target, but over here those details need to be fleshed out. The idea of any president playing the role of judge, jury and executioner tends to rub us Americans the wrong way.
So do we. We cant go around killing UK citizens willy-nilly. But when it happened/happens, there was/is less wailing and gnashing of teeth.
The law should aid defence and security not hinder.