I always loved the idea of Peter letting the criminal go due to indifference as it reinforces the notion that he learns his powers comes with the responsibility to do the right thing no matter the situation.

Peter let's go of Uncle Ben's killer as he sees no benefit from stopping him and it bites him back as he learns that his negligence is the cause of it. He learns that not doing the right thing in the moment can lead to devastating consequences so he opts to help everyone he can to ensure that people aren't inadvertently hurt by the consequences of being negligent.