The two simplest sugars are glucose and fructose. Ordinary table sugar is sucrose. Each sucrose molecule consists of one glucose molecule and one fructose molecule joined together. When you eat sucrose, the first thing your body does is break it down into 50% glucose and 50% fructose. All of these sugars occur naturally in many plant foods.
High-fructose corn syrup is 55% fructose and 45% glucose, plus some water to make it liquid. It is cheaper than sucrose because Iowa grows corn and Cuba grows cane sugar, and the USA has policies favoring Iowa farmers. It is easier because it is liquid.
I don't see how HFCS could be any less healthy than sucrose. It is essentially the same stuff once it gets into your body.
Update: Here is some new research:
Two papers in the journal PNAS in 2007 and 2008 showed that glucose and fructose act quite differently in the brain (hypothalamus) - glucose decreasing food intake and fructose increasing food intake. ...I don't know if this is significant or not. It seems to me that all good-tasting foods make me want to eat more, and bad-tasting foods make me want to eat less. So maybe that makes good-tasting foods fattening.
The fact that fructose metabolism by the brain increases food intake and obesity risk raises health concerns in view of the large and increasing per capita consumption of high fructose sweeteners, especially by youth.