Recently a researcher tried to make the case of the benefits of gene modification in people. One of his examples of what he considered desirable was decreasing sensitivity to pain. That is really scary. If you are less sensitive to pain, you will be less careful about injuring yourself, as in autistic people. The decay of fingers & toes in leprosy is not due to the disease itself, but to the fact that the disease kills the pain neurons, so people do not get the feedback that keeps them from repeated injuries. If you can't feel pain yourself, you will be insensitive to inflicting it on others.https://www.eurekalert.org/pub_releases/2016-12/du-apc112816.php
Public Release: 1-Dec-2016
Autism-linked protein crucial for feeling pain
Well-known autism and pain proteins are likely co-conspirators
Sensory problems are common to autism spectrum disorders. Some individuals with autism may injure themselves repetitively -- for example, pulling their hair or banging their heads -- because they're less sensitive to pain than other people.