Realism and Moral Authority

Writing in Commentary, Emanuele Ottolenghi notes that the Iranians have violated international law by executing Delara Darabi, who was 17 when convicted of a murder she claims she did not commit.

Ottolenghi then goes on to write:

Now, “realists” will argue that though a terrible thing, there are tyrants everywhere and we must realize we can’t impose democracy and human rights all over the place. It’s an attitude that one could come to terms with and understand — sort of — if it came from people who did not get so offended by water-boarding and other such practices. But this convenient contradiction should not be allowed to overshadow a central tenet of what a U.S. president recently called “the false choice between our security and our ideals.”

Why can't realists "realists" make this argument? It seems perfectly non-contradictory to me. Iran shouldn't execute little girls. America shouldn't torture people. What's the problem here?