It’s worth noting that cats are unlikely to be able to perceive sweet tastes. So while sugar is not toxic to cats, there’s not really any benefit to letting them have it, even as a treat.
On a related note, there’s a hypothesis that the mutation that caused them to lose the ability to taste sweet things in cat ancestors is what led to them becoming obligate carnivores, which is kind of interesting.
Heh, I knew a cat that would go through a pan of unseasoned cauliflower if you weren’t careful. Maybe every cat is born knowing something they have no clear way of understanding, like how tasteless things are food or how to move in four dimensions or what electronics are.
More seriously, the article I linked to suggests cats can taste things we can’t, so that’s a possibility.