It's its.
I think Pa Kent's rationale of trying to get Clark to not "expose" his true self makes Kal El's later choices and decisions even more heroic.
Here's his father telling him he shouldn't risk his life to save others, because people will not be ready to accept him, until he finds out the purpose of his having been sent to earth.
He's basically saying, wait a minute son, don't risk your life until you know why you have all these superpowers and can 1. deal with them and 2. better accomplish what you were sent here for.
Remember the flashback to when the other kids were bullying him and he doesn't fight back. Pa Kent can see what's going on, but he lets Clark decide how he should react. It's a way of building character and showing faith in his son. That lesson is reinforced when the fat kid who bullied him in the bus helps him up. It's a valuable lesson to know that people can rise above their earlier mistakes, that if you do good, it will come back to you. And to top it off, Pa Kent gives him a little speech about choosing which man he wants to be, because that man will change the world (IIRC).
So it's not that Pa Kent doesn't want Clark to help or save people, it's that he wants to make sure that Clark has the fortitude and wisdom to do it right when he presents himself to humanity as what he truly is: a god-like being from another planet.
Personally, I find that a lot more complex, true and satisfying than the usual "he was raised by good folks in nowheresville USA so he keeps himself in check".
Which is not to say that that was bad. It's just that I find this more convincing for this day and age. The naiveté of the old story doesn't seem to have much traction for me.