“Cis”, coming from chemistry, is the opposite of trans. So if you’re not trans, you’re cis. (Pronounced “siss”). I think the reason it is uncomfortable is because the assumption is that cis people are “just normal” in society and trans people are the one who are deserving of a label or an other category. To call non-trans people “cis” is to equalise the playing field and say that no one is “normal” but that there are cis people and trans people.
Some people feel like this constructs another binary, but at the end of the day I think that so long as we understand that a person can eventually come to know themselves as trans even though they once identified as cis, I don’t see a problem with making a distinction between people who are trans and who aren’t.
Even if you feel uncomfortable, trust that, unlike being trans, being cis doesn’t come with any structural discrimination and bigotry on the basis of being cis alone.
I understand who you feel about replacing the “D” with an “I”, though my “disorders” are congenital and “uncureable”. I’d have thought that a disorder in and of itself would communicate a certain state of uncureable-ness but… so be it. I feel like my whole life with my disorder I’ve been pushed toward being “normal” and being like everyone else. I think we should to a certain extent accept that different people will get to different points in their life instead of trying to force everyone to be exactly identical.