LOL - would you prefer to use a JCB?
I understand what you mean about a defect - I just find from a biological perspective its more of an evolutionary change is all

)
But yes, I think we are saying the same thing using different terminology LOL
As with regards to the blind/partially sighted - i used to consider these things a defect until I did more reading and discovered its genetic alterations and genetic imperfection. Defection is dependent upon your idea of perfection I guess.
*plays devils advocate*