Sure. People can contribute in those ways. And let's say, for the sake of argument, that childfree people contribute more because they have more financial resources and time to volunteer etc. That's certainly a good point.
But ultimately, if every person stopped having kids right now, and used their resources as their own to do with solely as they wanted - including altruistically contributing heavily to the good of society - within 70-90 years every single person would be elderly, and increasingly there would be no one to drive the trucks, or build the homes, or treat the patients, or relieve your pain, or lift your body, or make, sell and deliver your food.
What good are your financial contributions then? It's the act of creating the next generation that is the key - of making people that can do all the things you are no longer able to do.
I don't really care about the individual examples of people who wanted kids or didn't want them or neglected them or any of that; on an individual level you can justify any decision. But in general, globally, we need a younger generation. Not YOUR child takes care of YOU specifically, but the 'children' take care of people, in general.