C. Karelis's unusual theory of marginal disutilities

Charles Karelis has a quite unique theory and the thing is I suspect it’s wrong but cannot really prove it. You can read the article here:

http://www.boston.com/bostonglobe/ideas/articles/2008/03/30/the_sting_of_poverty/?page=full

Basically, if I understand correctly, his idea is the following. According to marginal utility theory, if I have 10 cars and one of them is stolen I’ll be much less
angry than if I had only one car and it was stolen. However, this works the other way around too: if I have 10 dents in the car (disutility), fixing one of them gives much less
satisfaction than if I had only one dent and had that fixed. So the kind of utility gained from fixing disutilities does not diminish, but the other way around. I think it must be correct, up to this point.

However the whole of the theory somehow still stinks, because I think the difference between gaining utility or fixing a disutility is entirely arbitrary. But how do I prove it?