E.G.

For each comment added to this post, the author’s friend will give a dollar to Oxfam.

It’s good that the author’s friend is going to give money to charity, but I don’t see why the amount should be related to the number of comments added to a blog post.  Doesn’t it make more sense to let the amount be determined by things like the person’s degree of moral obligation, the limitations of his personal finances, etc.?

Another, similar thing: the ACS’s Bike-a-Thon asks one person to agree to donate an amount of money equal to the number of miles another person rides on a bike.  (I participated in the Bike-a-Thon every year during elementary school.  It was a lot of fun.)

This practice of tying amounts given to charity to unrelated quantities probably has a number of psychological advantages.  For one thing, it gives people who may not know how much is appropriate to give to charity a way to determine a precise amount.  Some people, I guess, hesitate to give at all because they are afraid they might choose the wrong number.  For another thing, this practice can allow people to feel like they are directly participating in the work of the charity.  The Bike-a-Thon, for instance, creates the illusion that you are curing cancer by riding your bike around and around.