Domestic spying violates constitutional rights. More to the point, I don't want to support an institution with programs that violate my privacy, no matter what benefits such programs provide.
But isn't international spying is different? Honestly, I don't mind supporting an institution with an external espionage programs. Isn't in my best interest? Does it harm me? What are the concrete repercussions of spying on foreign officials? Are these officials really going to renege on international alliances because they have a chip on their shoulder? If they have anything to hide, it's by definition counter to US interests; if our allies are making plans behind our backs, I want our government to find out. (And to be totally honest, if our government is making secret plans behind our allies backs, I would want our allies to find out, as well.)
I'll repeat this, because it is a real question, and the answer could have a real effect on my opinion: What are the concrete repercussions of spying on foreign officials?