A pretty naive statement, especially because there is a rather obvious biological reason why genital shrinkage occurs in some people. Finasteride can shut peoples testosterone production down, which will cause genital shrinkage. It is by the same method as bodybuilders who go on testosterone cycles and don't end with a correct PCT to restart their own production, they often times encounter genital shrinkage. DHT is also responsible for modulating nitic oxide in the penis - so certain individuals with certain types of body chemistry may indeed respond very negatively to having their DHT depleted. And that is the start.
Explain to me how someone who was surgically castrated experienced a 20% penile shrink, yet this person experienced a 50% shrinkage due to finasteride. Something is off, right?