Where did the term "cis-" come from, anyway?
As for the word debate...I'm with agfrommd, we have to have words to make a distinction between people born in the correct body, and those who are in the process of changing their bodies...why? Because the "trans" people have different struggles than the "cis" people.
Surgeries, for one.
Acceptance--by themselves and others--for a second.
Work and social issues, for a third.
If I were to say, "Hey, I'm a woman and I have problems at work being a woman; they won't let me use the ladie's room", a cis-person would ask "Why?" I'd have to explain it's because I am not accepted as a woman, because I was born in a male body. So, we need terms that are universally accepted to identify people born in the correct body, and those transitioning to the correct body.
To deny it is to make communication difficult, if not impossible.
Myself, I would've asked why the group thought it was funny to make light of what is really a serious matter. (Would they have made jokes about African-Americans insisting on being called "blacks" instead of "Negroes"? Respect can only happen once acceptable names are used, imho)