I've thought that too, and it's hard to believe you really could convince yourself that your level of responsibility/guilt for the outcome is significantly less

I've thought that too, and it's hard to believe you really could convince yourself that your level of responsibility/guilt for the outcome is significantly less in the case you choose not to intervene even when you easily could. If the lever was some distance away (and certainly if other people were just as able to reach it on time) then not running to and pulling it seem to be a less culpable choice.