The catch is that the body likes lots of things that are awful for it. For instance drug abuse isn't limited to humans - some bears have gotten addicted to huffing gas to get high. [1] Quite cute if it wasn't so awful! The big issue is that in modern times a whole bunch of things are going wrong - testosterone levels (adjusted for health/bmi/age) are declining, IQ is declining [2], basically every single psychological disorder is skyrocketing, and much more.

And the reason why isn't clear. So the most likely reason is that we're doing what humanity has done repeatedly and endlessly throughout history and likely accidentally poisoning ourselves with some thing or things -- things that we believe to be completely safe. So a precautionary principle approach to consumption is to consider what we evolved with and sugar definitely wasn't that. Sugar only really took off in the 19th century. And various further refined sweeteners like high fructose corn syrup and other such things only took off in the late 20th century.

[1] - https://www.dailymail.co.uk/news/article-2294757/Bear-ly-con...

[2] - https://www.popularmechanics.com/science/a43469569/american-...