To many people, the words "penis" and "removal" do not seem fit to be in the same sentence, but whether they like it or not, this exists in many forms. Removal of the penis was something used by ancient civilizations to demonstrate their dominance. In was a convenient way of counting how many dead bodies were present, while humiliating them at the same time. Nowadays, it is more commonly used for severe cases of prostate cancer, though even those cases are pretty rare.
Castration is another form of penis removal. It actually refers to the detachment of the testicles, but often part of the penis is removed as well. This has been used for different reasons. For Italians, it was to conserve the high-pitched voices of the singers, who were often young boys. Castration has also been used to create a lower class of servants, who could not reproduce thereafter. In general, penis removal is an unpleasant occurrence. Few men willingly want to have their penis removed.
Voluntary vs. Involuntary:
Involuntary penis removal is an unusual, but nonetheless a present aspect in our society. Such cases can be kept private, but many of them turn very public as it is an area that somewhat interests people. The most famous case was made by Lorena Bobbitt when she cut off her then-husband's penis. It was reattached by surgeons and he has gone on to have a relatively lucrative career, but there is no evidence that this would the case for other such victims.
Voluntary penis removal, such as males who would like to become female, represents a small percentage of the world. Transgender people have a decidedly tough choice to make regarding an unwanted penis and many of them simply cannot afford the procedure as it is not covered by most insurance policies.