In a few key instances, that selfishness has been let totally off the leash - and the results have been enough to make even Rick question the wisdom of crossing his young grandson. Sure, like all kids, Morty has made some stupid, unthinking mistakes in pursuit of his own satisfaction which have had horrifying consequences - but more than that, he's been shown to have a hell of a vindictive streak, not to mention a tendency toward the selfishness that seems to run in his family. One could make the case that Rick has been a corrupting influence on Morty, but there's at least an equally strong case to be made that Morty is more like Rick than he (or we) would ever like to think.
