Let's not turn Spider-Man into an afterschool special. I think Spider-Man 2 had it right, in terms of having a theme, but not driving into your skull like Spider-Man 3 did.
I'm not sure how to condense it into a neat little two word package, but I think Spider-Man 4 should essentially revolve around the conflict Peter has within himself regarding the Lizard. I mean, we've got the Lizard, a savage, mindless beast who is occasionally killing innocent people, but Peter is also one of only a handful of people who knows that it's really Dr. Curt Connors, who he cares about and respects deeply. The Lizard is very strong, and not easily subdued, so a capture isn't simple.
Not only is he faced with his own crisis of conscious, he is faced with a public that becomes hysterical in their fear, and begins to resent Spider-Man for not bringing the crisis to a close more quickly, and begin to demand that the Lizard be killed (which of course raises a question within Peter; is he being selfish? he wants to search for a cure, but the longer he waits, the more people die; is the cost too much? is he putting his own desires before the greater good by continuing to spare the Lizard, despite the death and destruction he causes?).
Enter Kraven, a man more than willing to and more than capable of giving the public exactly what they want by killing the Lizard. Quickly, the conflict between Kraven and Spider-Man becomes well-publicized, and the media and public opinion sways in Kraven's favor.
So the Peter is faced with an intense internal conflict: personal moral crisis; conscious vs. public pressure; as well as a complicated external conflict: defeat Lizard, keep Kraven from killing Lizard, keep Lizard and Kraven from killing him).
I think that's more than enough to fill the moral theme quota.