superman american alien dealt with the topic in a similar fashion. it is really a conundrum. the kents were charged with raising a god and teaching him compassion and human values. they were also charged with teaching him how to be a human amongst men as well as an alien god who will one day learn how to fly.
it's easy to judge jonathan kent and act like he was supportive of letting those kids drown, but he wasn't. he didn't tell clark that he did a bad thing. he just warned them that his actions had consequences. and they did.
if you remember, pete ross and his mother showed up immediately after and wanted to worship clark like a jesus. now imagine that widespread and imagine what that would do to the psychology of a young man with zero world experience, unlimited power, and no one to show him any balance.
like it or not, the kents had to teach clark humanity along with his powers. otherwise, they run the risk of not providing him the moral compass he needs to not be a monster (like ZOD).
jonathan's lesson wasn't to not save those kids on the bus, or to let him die. it was to consider every action carefully, because every action will have a consequence.
superman cannot save everyone and remain clark kent. that's a lie the comics have told. one that the movie at least made an attempt to address.
whether it was successful or not is up for debate of course..