Yes, high fructose corn syrup is bad for you, because it is synthetic. It is also bad because it is in sweets and other things that do not have much nutritional value. It also does not taste as good as sugar. Sugar is at least a natural product, while high fructose corn syrup will inevitably make you die sooner.
High fructose corn syrup is a chemically derived sugar that your body does not properly digest. It was created as a way to provide a product for agriculture that would allow agriculture to become more industrial. During the 50s, with the prodding of state ag departments and the USDA, agriculture shifted toward more commodicized products that could be stored for long terms. Farmers overproduced products like corn, and the system needed new products like corn syrup to dispose of the excess. The process of making corn syrup is totally unnatural.
HFCS is derived from corn. It is a naturally sourced, not synthetic, sweetener. It is metabolically equivalent to table sugar. HFCS, like table sugar, contains fructose and glucose in a roughly 50/50 blend, though it may vary a bit (about 5%) either way. Any health problems regarding either of these sugar sources are because of the amount consumed, not because of any difference between HFCS and table sugar.
Some published, peer-reviewed research to back up my claim:
"There is [...] no direct evidence for more serious metabolic consequences of high fructose corn syrup versus sucrose consumption.
"[HFCS] is not meaningfully different in composition or metabolism from other fructose-glucose sweeteners like sucrose, honey, and fruit juice concentrates."
"[...] [A] broad scientific consensus has emerged that there are no metabolic or endocrine response differences between HFCS and sucrose related to obesity or any other adverse health outcome."