I'm certainly no expert but from the research I've done, High Fructose Corn Syrup is what's bad for you since it's not natural and it's processed. So the body doesn't really know how to process it or what to do with it and this is where it starts being stored as fat rather than having it processed and exit out of your body like natural sugar.
From a personal experience, once I cut out regular soda's with HFCS, I definitely lost some fat which was noticeable. However I continue eating things with natural sugars(just at moderation) and I'm still able to keep in shape with low bmi, just going for walks and weighlifting every other day.
I go for what's sustainable and still let's me live life with all the pleasures it can offer. Man has lived with sugar for years and it wasn't until the past couple decades or so where this obesity epidemic has started. I personally don't think sugar alone is what's causing this.