It has nothing to do with whether you see perfectly or not ....
Its because of the RISK of retinal detachment!
The higher the myopia the greater the risk of you suffering from a retinal detachment.
Having lasik re shapes the cornea to compensate for the myopia but it does NOT change the shape of the eye that causes the myopia in the first place...
Therefore having 20/20 vision is one thing but if you 're at 37,000 ft in the air and suffer a retinal detachment you're in serious trouble.