I think that's fine from the author POV. They are not trying to impose their views onto others, they just don't want to be personally contributing.

The "Even if I wasn't doing it someone else would" defense is used to justify all sorts of bad behavior by people. If you think something is wrong and you have the choice, the least you can do is not contribute to it. Especially if it's a hobby project for you where you don't have any incentives to compromise your principles.

It's the root of many cognitive dissonances. "if I wasn't working on this addictive and toxic social media platform for a very good salary surely someone else would do it instead and the only difference to the world is that I would get less money".

This sort of jutification pops up everywhere. "I'm not really doing something bad because if I wasn't there it would still be done.".

Maybe there is a game theory research on this but basically the end point is a situation where everyone think some action is ethically wrong or has bad outcome for the group but they are still doing it because they don't know what others think and they assume one or more have less ethos than them.