To me it's more like, well, we participate in a society that (unfortunately) believes in private property, and I think on some level, in that context, it would seem rude to a stranger if I lifted their joke without credit. So if it doesn't diminish me, I should make sure they're credited/boosted, for the same reason that I'd want them properly compensated for their labor. But on the other hand I see what you mean. Saint Peter is not going to call me out for potentially narcissistically taking credit for someone else's obvious Muppets riff.