I don't see a problem with it. The game's $10, at least 4 - 5 hours of gameplay whether you play it or not and it was clearly enjoyed by them. It's just a source of entertainment. It's like saying you shouldn't pay to go to a theatre or anything like that, which is far more expensive for less hours of entertainment.
True but then you have to think of all the other things you could have gotten with that 10$ and weather or not it was really worth it and if you spent it efficiently
I could have gone to subway and bought two foot long's etc. or I could have wait for the humble bundle of this game or you could have waited for a humble bundle deal which would have saved the money but meh either way it's not like I'm a banker trying to help people save money what do I know ?
And youtube also has free etertainment if you are talking about just gaming wise I under stand then.