Not to muddy the waters, but a couple years ago I ran into this quote from Mahasi Sayadaw:
In this world nothing happens to a person that he does not for some reason or other deserve. Usually, men of ordinary intellect cannot comprehend the actual reason or reasons. The definite invisible cause or causes of the visible effect is not necessarily confined to the present life, they may be traced to a proximate or remote past birth.
However, in the same essay (http://www.buddhanet.net/t_karma.htm
" onclick="window.open(this.href);return false;) he goes on to present a rather complex intersection of kammic and non-kammic factors, so is it possible his use of "deserve" was a mistranslation? It hardly makes sense to say a farmer "deserved" a crop failure if it was due to Utu Niyama, although of course there could be aspects of the farmer's situation which he/she brought about.
I usually think of kamma as a general principle. The Skepdic folks are using loaded examples to try to discredit the general principle. But with just about any
general statement, we can point to apparent exceptions, anomalies or problem cases. Since we are not Buddhas, we don't know all the factors and how they may have combined to produce a particular situation. The point is to apply the principle to our thoughts, speech and action, not to engage in retroactive "kammic diagnoses" as to why someone's life turns out the way it does, or why some horrific atrocity took place. Kammic law, within our limited understanding, can only be an approximation.
I doubt many reasonable people would say that our experience of the world is without any moral dimension. Secular humanists would say that human morality intersects with natural law to produce a result. Buddhists would say that kamma intersects with natural law to produce a result. (If we want to split hairs, we could get into an argument over whether kamma "intersects" with nature or "manifests" via nature). Humanists would say that some things can't be explained in moral terms; Buddhists would say that the intricacies of kamma are imponderable. Just how far is the gap between these positions, really?