You dont owe this world a thing.
You should consider letting kids die to protect yourself.
Yup, nothing Randian about that. Total coincidence that same director wants to make a Fountainhead movie.
It's important to look at both of these in context.
In the MOS scene, Jonathan starts out angry at Clark; slamming the door on his way out, the way he delivered "We talked about this, right?". He's annoyed that Clarks secret has been put at risk and scared that his son might now be in danger.
When Clark says "What was I supposed to do, just let them die?", Jonathan pauses, he's speechless for a moment. He realises that he's made a mistake, and is ashamed.
Consider the way Costner delivers that "Maybe", he's quiet now, and looking at the ground, he isn't saying yes, he's saying he doesn't know.
Jonathan is considering a scenario where letting a small number of people die now, will save many in the future and he's struggling with that moral dilemma.
He knows that Clark did a good thing by saving the kids, but he's also a parent scared for his child, and someone who feels the weight of history on his shoulders.
Jonathan makes clear he knows Clark is going to radically change the world, so he's trying to make sure it doesn't go wrong. He's trying to impress upon Clark the importance of being very careful how he uses his powers.
I think a lot of people have taken "Maybe" to mean yes, but it very much doesn't, it means I don't know. It's a very realistic, human response, he wants to do good, but isn't sure what the best way to do that is.
For BVS, the full quote is:
"Be their hero Clark, be their angel, be their monument, be anything they need you to be.
Or be none of it. You don't owe this world a thing, you never did."
Martha tells Clark he has a choice, she doesn't tell him what to do, she let's him make his own decision. She tells him he has two paths infront of him, without saying he should follow.
Martha is saying that if he's going to wear the cape, he's going to need to accept that fact that people will idolise him, and he'll need to try to embody the highest ideals of humanity.
And that if he can't do that, he needs to stop.
Martha believes in Superman, that he does good and is helping people. But she's also a mother, who is seeing her son being publicly criticised just for trying to save lives, accused of murder, of being a threat to the human race. It's completely natural for her to feel angry, she loves her child and is protective of him, of course she's going to feel some resentment towards the way he's being treated.
Martha is conflicted, isn't sure what the right thing is.
Again, it seems a lot of people took this as Martha saying "be none of it ", which isn't the case she just reframes Clarks options for him.
Martha isn't telling him to stop being Superman, she's letting him decide.
Both of these are examples of a parent trying to help their child with a difficult decision that they are both struggling with.
It's different from the super-hero norm, where there's a Jor-El or an Uncle Ben who tells the hero in no uncertain terms what the right thing is, where right and wrong and easily distinguished.
Rather than the hero just being given their marching orders by a perfect role model, the Kents are good people but fallible, the don't have all the answers but are trying their best.
MOS and BVS show that the right choice isn't always easy to determine, that real people with pure intentions have trouble finding the best way to help.