Last year I made a post that wasn't particularly eloquent or revolutionary to my mind. But it appears it bears repeating given the events at Pam's House Blend (discussed here: A Point About Cis).
Yes. I am a cissexual woman. Cisgender even, for the most part.
To use these words and to acknowledge my status is not an attack on cisgender people.
To have a label instead of just being "default" is infinitely preferable to me.
Being ok with positioning yourself as "default" (which is exactly what only ascribing labels to "those other people" is) is not the work of an ally. Nope, not even a little bit. And justifying that behavior in others, enabling that behavior, not so cool either, to be perfectly honest.
And if you're coming across this word for the first time, that's ok! It's ok to be ignorant, just so long as when you discover you are, you take steps to become not so. Google is your friend!