The FAQ is still there: https://web.archive.org/web/20200125070811/https://www.reddit.com/r/GenderCritical/wiki/faq

Why do you use the terms “TIM” and “TIF” instead of “MtF” or “trans woman” and “FtM” or “trans man”? Female and male refer to biological sex, which is a characteristic that cannot be changed in the human species, regardless of what hormones one takes or surgeries one undergoes. Since sex cannot be changed, if someone transitions, they are not transitioning into something other than their birth sex. A “transman” is still a female, and “TIF,” short for “Trans Identified Female,” denotes that while someone may be transgender, they have not ceased to be female (and vice versa for males).

Why do you not use the term “cisgendered” or “cis” here? The word “cisgendered” is used by adherents of trans ideology to mean someone whose “gender identity” is “aligned with their birth sex,” or “anyone who is not transgendered.” However, these definitions are not synonymous. The ideology behind the term “cis” implies that everyone who is not transgender is “comfortable with their gender” and feels that they fit into their assigned gender, when this is not reflected in reality. Gender is a social status and social role, and its prescriptions are restrictive to both men and women. This study on gender identity in “normative” individuals found that:

36.6% of our [non-trans] subjects reported that they sometimes feel as the ‘other’ gender

63.7% reported that they sometimes wish to be the ‘other’ gender

49% did not always wear clothes ‘appropriate’ to their sex &

41.9% were sometimes discontent with their sexed body.

There is not a general sense of contentment and identifying with gender among supposedly “cisgendered” people.

Furthermore, to feminists, the assertion that all people naturally identify with gender, which is what we call sex roles and sex statuses, is sexist and naturalizes the oppression of women by men. In a patriarchy, sex statuses are organized as a hierarchy, which elevates men, and the attributes associated with men, over women and the attributes associated with women. Promoting the idea that women and men naturally identify with gendered constraints is opposed to feminism, which asserts that people do not naturally align with the oppressive, socially imposed hierarchy of patriarchy, but that we're socialized into conforming to it.

By calling a woman a “cis woman,” the speaker is implying that normal women naturally conform to the female sex role, and that any women who don't identify with an inherently sexist role are actually not women at all. It's defining women by sex roles, which is misogynistic and anti-feminist.

See this essay by Rebecca Reily-Cooper if you are interested in examining this topic further. Here is an excerpt:

I am not permitted to deny that I have a gender identity at all. But this is in itself oppressive. It makes false assertions about the subjective experience of many people – people like me who do not feel as if we have a deep, internal sense of our own gender, and whose primary experience of gender is as a coercive, externally imposed set of constraints, rather than an essential aspect of our personal identity. It forces us to define ourselves in ways we don’t accept (and, as I’m now learning, if we refuse to define ourselves in this way, this is attributed to bigotry and a lack of empathy for trans people, rather than a reasonable rejection of what being cis entails). If “cisgender” were a description of a medical condition, characterised by an absence of sex dysphoria, then I would accept that I am cis. But if cisgender is a gender identity, which it appears to be, then I am not cis, because I do not have a gender identity. I am a woman. But it’s not because deep down, I feel like one. Because deep down, I just feel like a person.

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