I have to agree with e that an economy as a part of a nation and not as a system is driven by the support that is given by people who spend their money. Putting aside the fact that the economy will move on, he is just saying that he will be a productive member of society and of the economy if he buys video games, and in saying such he is, in fact, correct, no matter how much you say there will always be a demand. Just like you can say there will always be a demand, I can say that if everybody didn't support an industry like e is describing, the economy would collapse. Or, rather, the economy would fail to exist.
The economy as a system that is nation or worldwide will always, other than in extreme doomsday situation, have a demand, but you can't use that to say that by providing demand you aren't helping. Because if everybody took that to heart and didn't help, you wouldn't have ANY demand. Just because in theory there will always be demand doesn't mean that the things supplying the demand are worthless or null because you can count on them, they are still providing a service whether or not that seems useful.
If it's raining and I point at a drop and say it isn't helping because I have all the other drops, and then all the other drops stop coming, then I'm pretty screwed (assuming I need the rain). Likewise, just because there are billions of other sources to the economy, that doesn't make his contribution less useful, especially to his local economy.