I agree, consumption of sugar at normal rates is not a problem if it's not on top of meals that already fulfill your daily energy requirements.
There are a few issues that I can see with sugar though: refined sugar is added to almost all the food you buy for your breakfast/lunch/dinner without you knowing, sugar is addictive, refined sugar doesn't give you any benefits (health or otherwise) unless you're an athlete or don't have access to enough food to cover your energy requirements.
I think the main issue is that sugar is very addictive and most people just can't stop consuming it. The more you eat the more you crave. And it's very easy and cheap to get it. Not sure if focusing on sugar will do any good to prevent obesity but it seems to be the low hanging fruit at the moment.
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