If is a certified by a doctor that is a medical contion it might be understandable. What about guys which are 1.90 m? Their legs cannot fit in the crampled space of economy.
If you are uncofortable in economy buy a business class ticket, alot of space. Does a 6 month pregnant woman have the right to an extra seat? The whole story is absurd.
That could be streached to the point that an obese when buying clothing shall pay the same price of a slim guy. Or if a big mac is not sufficient he can get another free because is still hungry!