Let's face the truth: There is no shortage on games. Steam Sales provide a plethora of cheap games and, f2p aside, there are even a lot of free games. In a bunch of countries prices below $ 5 somewhat qualify as 'almost free' in my opinion (and I respect different opinions).

how much good would this actually do if I did it

Please, I beg you: think outside the box. Helping people in the real world is more likely the real deal. Help your neighbour with his leg broken: Take his dog for a walk. Help an elderly woman in your neighbourhood with her groceries. Become a medical doctor and heal people. Help a disabled, poor person to learn reading and writing.

This is my opinion, and again, I respect different opinions, so don't kill me:

• Giving away products for free does not automatically mean helping anyone. Just think about the F2P model and the addiction this model thrives on.
• How can games help people? I've seen bold claims, but I don't see much helpful games. I don't blame anyone, but calling games helpful is just the wrong category in my opinion (for 99.9999%). Not trying to discredit games, not at all. Just not buying the 'helpfulness' claim.

Can this be called a generous use of my time or am I just being selfish?

This universe is large enough to host more than the two aspects of selfishness versus generosity. There are shades of grey, there are even colours. I believe you can be both selfish and generous at the same time. In fact, a lot of people are 'generous' because they are selfish. Why do you think you can use so many Google services for free?

Don't fall prey to the weird assumption that you must only do things that are not selfish, that are generous to society or a group of people. Don't fall prey to the notion that giving away things is always a divine act. That's a supposition that should be questioned. Instead, think about the outcome and the impact: Feeding the hungry will affect their hunger. Treating a broken leg will help a person walk again. But what impact does one more free game have to a single person or to a group in our society? A treatment against boredom? Well, people have Facebook, Instagram, reddit, TV shows. 24/7.

If your game does something unique, one thing that really makes an impact, then go ahead, don't let me stop you. A game that will raise funds for good cause, a game that helps cure cancer... But please be honest about the impact: If you create a game claiming to educate, a game claiming to teach how to code, then probability is high the claim cannot be fulfilled. It will stay just that - a claim. And even if it does a thing, like teach how to code, it might teach incredibly bad and useless habits. And the teaching part might be incredibly slow as well, compared to just about any other teaching method.