Man of Steel is a much weaker movie than Watchmen. Jor-El only saving Kal-EL has two reasons. He is kind of the only reasonable voice in Krypton in pretty much every version of the story. It would have been hard to convince and get anybody else involved.

Even more important reason is the natural birth. Everything wrong artificial birth can be seen in Zod. When it is an artificial birth it's like making a carnivore. You are not going untrained its hunting instinct and make it vegan. That's why Zod is doing what he is doing. It is what he was made for. Zod and the rest are practically just NPCs.

For better or worse Kal-EL has a choice. He starts off Tabula Rasa. He is free and he is the new beginning.

Because Kal-EL has moral responsibilities and must become superman.

If we forget the existence of any DC material other than MoS, Kal-EL is practically brought up to not be superman. Even his father's death was changed from a heart attack to illustrate this point. You could say that after the church scene Kal-EL takes a leap of faith and become "Hope" (The S on the chest)

It's still not Zack Snyder's best work. But it is one of the best superhero movies out there.