I realize this post is a couple of months old, but ran across it and thought I would offer another perspective. I agree "cis" plays an important role in identifying the unmarked "default", and I used to happily call myself a cis woman, but I've learned recently that there's more than one definition floating around and not everyone who uses the term thinks it just means "I don't consider myself trans". Specifically, it sometimes gets used as a synonym for gender-conforming or gender-normative - here's a definition (http://gender.wikia.com/wiki/Cisgender) that identifies a cis person as matching expected gender *roles*. And under that definition, "cis" is both inaccurate and personally insulting to me, as it erases a good chunk of painful personal experience. (I am not a feminine person, I work in a male-dominated field, I am very familiar with sexism both open and subtle, and I absolutely do not identify with the "behaviors and roles generally considered appropriate for my sex".)

If the other people protesting are doing so for those reasons (and I know some are), perhaps it's not surprising it's mostly (feminist?) women who object: traditional feminine gender roles and stereotypes are quite a bit more constraining and diminishing than those for men, and a term that translates to "you're happy fitting into sexist stereotypes" is indeed both insulting and a huge presumption when used about someone you don't know.

But yeah. I *want* "cis" to just mean "I am generally okay with my sex assigned at birth" (language for this is useful!), but since I ran into people using it as "if you're cis, you're generally okay with all the cultural baggage associated with your gender assigned at birth", I've been more uncomfortable about declaring myself a cis woman.