Granted, I agree with you to a point and I don't see any reason you are downvoted/beside the obvious "don't be so negative" point, though I will upvote you, I feel this conversation is important/. At the same time it is extremely easy for you to use these articles/posts even in your CV and in building in your brand. Of course, you might not need that, but there are still a lot of uses including showing them to your future kids or thinking about how your writing changed someones live.
Leave that, there are specific content, which I have no issues being behind a paywall. You might put it behind a paywall/e-book/, show me that your content is useful to me, I will pay you in a heartbeat. Of course this is something that will take even more time.
To your point above spending time with new things or friends/family/working, I don't think that the author wanted you to stop doing them. Again he is asking you politely, do that if you have free time AND you are willing to help some complete strangers online. It is not something everyone would want to do and this is completely okey.
Also, I think there is something to be said about the whole "learning as you teach" mentality. Often times I find myself explaining something (which I've done a hundred times) to someone (who has never done it before) and I catch myself saying things that I had not paused to reflect on before; or, I find myself finding even better ways to do things as I explain them to someone else. Those are the sorts of benefits that might be in store for yourself, without any consideration to mutualistic benefits.
Guilty as charged :)