Why is it a sign of contempt to say someone's name is "mud?"

The man who assassinated President Abraham Lincoln, John Wilkes Booth,
broke his leg during his escape from Ford's Theater. Booth stopped by a
country doctor's office, who knew nothing about the assassination; after
treatment, Booth went on his way. After the doctor heard about the
assassination, he notified the authorities and was put in jail for his
efforts: he was accused of being a co-conspirator. The injustice was
later recognized, and he was subsequently pardoned by President Andrew
Johnson.

This doctor's name? Samuel Mudd. Soon after the assassination it
became an expression of contempt to say your name was "Mudd." Over
time, people have forgotten "mud" is actually "Mudd."