This may be scientifically unproven, but I'm a believer that the negative effects from fruits come from all that sugar in them.

I doubt even a committed frugivore gets close to the doses discussed in that article. Oranges, for instance, are quite rich in vitamin C, but you'd still have to eat about 30 to get the 3000mg dose described. And as ValentineC says, the sugar in all that fruit is probably more significant.

Everything is "poison" it just depends on the dose.