Unpopular opinion: It actually isn't Peter's fault that Uncle Ben was murdered
At least pertaining to the general "with great power, comes great responsibility" concept of Spider-Man's origin story. Peter at the time of Uncle Ben's death, didn't or couldn't have really known the full extent of his spider-powers. All that we know for context, is that he defeated a professional wrestler, when he otherwise shouldn't or couldn't have.
Peter isn't as of yet, out there playing a vigilante, so it isn't like stopping criminals is in his personal wheel-house or whatever you want to call it. It's within justifiable reason, that any sensible person, would allow matters such as armed robbery in the hands of the police.
And yet, we're asking a kid, I mean literally a kid, who isn't even bulletproof, to go after a criminal, when that's not even a job or duty that he's signed or trained to do. Peter couldn't have possibly known or suspected that his uncle was going to be caught in the crossfire (both literally and figuratively).