I understand that high fructose corn syrup was found to have detrimental effects on peoples' health. Why is this so?
Besides a lot of propaganda there is not much evidence that high fructose corn syrup (HFCS) is more dangerous than normal sugar. Lets have a look at the sugar in detail:
HFCS is produced from corn and is originally a glucose syrup. Since fructose is obviously much sweeter, the glucose is converted enzymatically into fructose (see here for more details). Before the use in food production additional glucose is added to the syrup so that typical syrups contain 55% fructose and 42% glucose or 42% fructose and 53% glucose (the remaining % are water).
If you look at saccharose (which is our ordinary sugar) then this is a disaccherid which is build from one molecule of glucose and one molecule of fructose. The enzyme sucrase breaks this molecule up into one molecule of fructose and glucose each, so reaching a 50%:50% ratio between the sugars.
As the ratios are more or less the same, it doesn't matter for the human body, where the sugar come from meaning that in this context it is more too much sugar in the food than a problem with HFCS, as also this study suggests:
Fructose itself is not without problems as this induces the production of fats in the liver, but again, it doesn't matter for the body, where this fructose comes from:
For further reading I can also recommend this article on Gizmodo:
The following study abstract of "Consumption of high-fructose corn syrup in beverages may play a role in the epidemic of obesity" copied from http://www.ncbi.nlm.nih.gov/pubmed/15051594 seems to address your question. I added a paragraph break; the second paragraph seems most relevant to me:
Fructose has a special characteristic that other sugars do not have: its absorption in the human intestine is not regulated, as opposed to glucose, for example.
The important implication is that all the fructose you consume will end inside your organism, either used immediately or stored as fat. Other sugars will only be partly assimilated, or will require more energy to assimilate. If you take the example of glucose again, a glucose molecule requires active transport (meaning consumes ATP, the most basic fuel of your organism) to transit across the intestinal wall. Fructose is absorbed via free transport (i.e. no ATP consumption).
This claim can be verified by opening any human physiology book, and while it is debatable whether fructose itself is deleterious, increasing the sugar amount in an already sugar-saturated environment clearly does not seem a good idea to me.