In the past there was such a thing as returnable bottles. You would pay a bottle deposit and you would get your money back when you returned the bottles. If you never returned the bottles would that constitute stealing/theft? Isn't the keg just one big returnable bottle?
But I returned the bottles.
I think that the black and white moralism doesn't always apply.
It's one thing to not return a keg and turn it into a keggle.
It's a different thing for people who have bought kegs that are already repurposed.
I wouldn't lose sleep over it, but I also wouldn't purposely steal a keg.
And I know for a fact that I don't have a 100% record for returning returnable bottles. I'll bet a whole batch of beer that Denny doesn't either.