I don't see how Superman going back to Krypton searching for survivors is something stupid.
Because Superman wouldn't do that. Find one time in the comics he did that. The closest I can think of is when he left in exile, and that was because he felt he could no longer serve as Superman. He also left Supergirl in charge of protecting Earth as he didn't want to leave it unprotected.
Superman, when written as he is supposed to be, isn't the type to go off on a five year journey at the expense of all his personal relationships because of some half baked, poorly explained rumor he heard from unreliable Earth science. He's smarter and more responsible than that.
And how was he being irresponsible to Lois about the child if he didn't know she was pregnant? Yes, he left without saying goodbye to her, but in his mind that was the only way he could go; if he had told her and she asked him to stay, he wouldn't have gone, but he felt he had to go. In other words, he was really torn, he acted like a real human being. He isn't perfect either.
Let me ask you something. If a man is in a sexual relationship with a woman, doesn't he owe her some modicum of respect? Just the slightest courtesy like, say, telling her he will be leaving for five years? That he might not be back? You know, to keep from breaking her heart and having her worry and think all sorts of terrible things during said five years?
That is how Superman was irresponsible to his son. Even if he didn't know he existed, he wronged him before he was ever born by not giving a damn about Lois' feelings. Oh, so she might ask him to stay? He might not go then? Well then maybe that would have been a sign that going would have been a stupid thing to do. But maybe Lois would have still been mad at him? Then Superman must have very little confidence in Lois' ability to act as an adult. If he absolutely had to go, and she loved him, she would have understood and been able to raise Jason as Superman's son instead of having another man think he's the father, thus hurting him when he eventually finds out.
And before you start in on the line of logic that I know is coming, no, I don't expect Superman to be perfect. But Superman shouldn't make such simple mistakes. Hell, I wouldn't do that kind of thing. So how can I be more moral than Superman?
You know, I can sum up all of this in one sentence. Its not just his powers that makes Superman super. The people behind the next movie would do well to remember that.
If may not be your ideal Superman behavior the way it happened, but he didn't really abandon his son since he didn't know he had one in the first place. Besides, this type of story has happened before in other mythologies like the Greek one with Zeus and Hercules for instance. They did it first and most people are ok with it. I'm no 'Superman purist' either so I find the way they did it in SR an acceptable one.

I really wonder if the next film will present Superman like such a perfect being in every way... can't wait to hear the fanboy reactions.....
Just so you know, Zeus and Hercules in traditional mythology are kind of jerks. Zeus turned a woman into a cow and had sex with her. So...not really the best comparisons.