I enjoyed the article. Many comments here on HN seem to be missing the point.
The author isn't bashing on "hobbies" and is not even bashing on "vanity activities". S/he is merely challenging us to acknowledge them for what they are. Stop kidding yourself.
If you churn credit cards (for example) and are one of the 10% that can make it truly profitable, then good for you. The other 90% are probably kidding themselves. Same for the other examples. The author is encouraging a self-sanity check. Are you in the 10% or the 90%, and wherever you land, are you okay with that? If not, you may want to reevaluate, pick something else, or make peace with it. It's better than kidding yourself.
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