LABD,
If I were to guess, It think that is because we see realize that there are emotional differences between boys and girls and we see it in two ways. One is the moral/legal way, and it is correct, because this woman abused her position and was in an unequal sexual relationship, which is why it is called statutory rape. Also we can't forget how hurt the newlywed husband of this creepy woman must feel.
But at the same time, we realize that for an heterosexual adolescent boy, he will almost certainly view any sexual contact with a female teacher as a conquest, or great achievement. And as conquests go, this was the freakin Roman Empire of Sex for the kid. Sadly, it may also tarnish his view of women as life goes on.