It's obvious without math that if you spend time helping people instead of having fun, more people will be helped and you will have less fun.

This is true, but it is not the only point of the post. I thought the post was an attempt to quantify these consequences--to find the marginal cost (in lives) of time. Isn't this a more worthwhile pursuit than the one you've cited?

This is a trade off that almost no one makes or will make.

I assumed this was the impetus for the post. The author must know this already, or s/he would not have titled the post so provocatively.