I love San Francisco, but when I visited with my wife she was really frightened in some of its streets, specially in downtown.
Don't get me wrong, but I wouldn't recommend walking near United Nations Ave. which is very close to the San Francisco Opera. We have gotten there with a romantic idea since we have seen it in a very old movie, Pretty Woman, when the guy takes Julia Roberts to watch an opera, in a private plane all the way from Los Angeles. Now we wonder how they didn't get robbed in their way to the theater.