It’s not a silly request. “Slave” is a very specific term that is highly emotionally charged. There are plenty of alternatives which convey the intended meaning just as clearly without the offensive connotation.
Imagine if one were to insist on referring to “male” and “female” connectors as “cocks” and “fuckholes”.
Imagine if one were to insist on referring to “male” and “female” connectors as “cocks” and “fuckholes”.
This is not a hill worth dying on.