because in his own country, and
in most parts of the US, it wouldn't have been. Anyone sensible would check, of course, and it would seem risky to take a girl's word for it that she's 17 in this situation anyway. But to say "in order to break the law" implies he knew beforehand it was illegal, which I haven't actually seen in a report yet.
Yes, what he did was illegal, but that doesn't mean people can't suggest that it should have been legal. 18 is a surprisingly high age for being able to consent to sex without parental permission. For instance, a 2004 poll said
43 percent of American 17 year olds had had sex.
I suspect that's why this has generated a lot of comment here - because people don't expect California to be so puritanical. FWIW, when the age for buying drink comes up, many DUers will always say that 21 is ridiculously high. It's just that's not the subject of this thread.