The corn plant is remarkably resilient to damage, especially early in its development. A single event that damages above-ground leaf tissue (say, frost or hail) does not often result in plant death unless the plant's main growing point is also damaged. However, repeated above-ground injury (say, from repeated sandblasting or severe leaf scarring from flea beetle activity) from the time the seedling emerges until the plant is well-established may result in plant death.
The key phrase here is REPEATED INJURY. Damage to green leaf tissue essentially destroys part of the photosynthetic factory of the corn plant. Less energy and fewer carbohydrates are produced, resulting in greater dependence on what's left of the kernel reserves to sustain the developing seedling.
A young seedling (say, from 1-leaf collar stage to 3- or 4-leaf collar stage) that is continuously and completely defoliated will survive until the seed reserves are used up. Even if the seedling survives, the shortage of available energy and nutrients will stunt the development of the nodal (permanent) root system. Subsequent growth of a seedling that survives repeated above-ground injury may be stunted because of the poorly established nodal root system.