Something that is not discussed very often is that a kind of food can be good and bad at the same time. It can be good for your (Darwinian) fitness: more reproduction of genes. But it can be bad for long term health.
I think fruit could be considered to be like this. Fruit could cause beneficial nutrients (energy, phytochemicals, ...) that put our organism in a 'go-and-reproduce-now-is-the-time' modus.
This could (partially) explain why most of us like fruits: ancestors who liked fruits reproduced more offspring, even at a cost. Darwinian medicine talks about these trade-offs quite a lot.
(edit: just adding something to the discussion here, not saying all of the before mentioned answers are wrong, quite the contrary. My two cents on fructose: the poison is in the dose)
