> Most people would even shut the door if they weren't around. Same principle.

This is a poor example because finding bugs requires a lot more effort than giving a door a push (which I find a little spurious - I wouldn't touch my neighbours' car).

There is in practice an almost infinite amount of things you can donate time to and all else being equal (for example, they're all password managers) I doubt you'll convince most people by telling them they should do it because "it makes things better for everyone", they could be making everything better for everyone and still getting paid - that's the superior option. Even if I think you are correct.