There is as much protein in broccoli as there is fiber in apples.
To get your daily suggested intake of fiber (30 grams), you'd need to eat almost three pounds of apples a day.
I fail to see the harm. If I did feel wild one day and decide to down a dozen apples (I'm not sure I physically even could), I'd meet my fiber RDA for that day, and still have only eaten 504 calories worth of carbs.
You may object that I'm not getting any micronutrients this way, but most sources of micronutrients are nearly irrelevant calorically, so they don't really matter when you talk about capacity planning for macronutrients and calories.
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.
Some fruits may be not much better than candy in that the sugar can metabolize quickly, but apples aren't one of those despite their fructose content.