The harm is that the apple is acidic, damages tooth enamel over time, its nutrition value comes only from sugar (most of which is fructose), and it's not actually filling. Ask any fruitarian how soon after a meal of fruit they feel hungry again.
Seeing no harm in eating apples is like seeing no harm in eating candy. Sure, eating a piece of candy once is trivial -- but you're insisting on candy as a part of my diet, not as an incidental, rare snack. Eating candy only has downsides.
Seeing no harm in eating apples is like seeing no harm in eating candy. Sure, eating a piece of candy once is trivial -- but you're insisting on candy as a part of my diet, not as an incidental, rare snack. Eating candy only has downsides.