Agave nectar is one of those silver bullets that’s appeared, mostly in so-called health foods, in the wake of increased public consciousness about high-fructose corn syrup. Don’t believe the hype, processed sugar is processed sugar, whether it comes from corn, cane, beets or cacti. - via Salt & Fat

Agave nectar consists primarily of fructose and glucose. One source gives 92% fructose and 8% glucose; another gives 56% fructose and 20% glucose. These differences presumably reflect variation from one vendor of agave nectar to another. Due to its fructose content and the fact that the glycemic index measures only glucose levels, agave nectar is notable in that its glycemic index and glycemic load are lower than many other natural sweeteners on the market.

However, the extremely high percentage of fructose can be deleterious and can trigger fructose malabsorption, metabolic syndrome, hypertriglyceridemia, decreased glucose tolerance, hyperinsulinemia, and accelerated uric acid formation - Wikipedia

I think the lesson to be learned is that unless you're getting your sugar naturally from unprocessed foods its probably bad for you. People need to stop cheating themselves in their diet. The answer isn't to invent some new kind of chemical sweetener so we can all enjoy our cupcakes and not feel guilty about it. The answer is to stop eating sweets and start eating well.