If people ask you adversarially—rather than genuinely curiously—why you identify as a man, that in itself is already a difficult position for you to be in. (Cisgender people are not socially expected to answer this question routinely, of course.)
The adversaries who have hardened their anti-trans ideology will never be satisfied by any answer you give. Their argument goes like this: "Masculine" and "feminine" stereotypes are limiting and oppressive. Therefore, trans people shouldn't argue they feel or behave "like a man" or "like a woman" because "masculinity" and "femininity" are culturally oppressive concepts and are not even objectively real, and thus "masculinity" and "femininity are undesirable benchmarks for people's personal identities and behaviors. "Man" and "woman" language should, instead, only be used to refer to people based on their genitals at birth. [That is what they say in their anti-trans arguments.]
There are a number of problems with their line of argument.
1. It doesn't reflect how they actually perceive and refer to gender. They do have cultural understandings of gender (conscious and unconscious), and they invoke these stereotypes and assumptions (directly and indirectly) all the time in their own lives for their own benefit and comfort. When they harass trans people, they suddenly deny having any baseline understandings of gender—i.e. they dissimulate about themselves to facilitate their harassing behavior. Claiming that they have no knowledge or beliefs about gender and that they are pure blank slates (while they simultaneously assume trans people to be full of wrong biases) is a conveniently simple way for them to avoid subjecting their own beliefs to the same kind of scrutiny that they announce they are happy to apply to trans people's beliefs.
2. Because their line of argument doesn't even acknowledge that they have (or could possibly have!) any beliefs about gender, neither can it go on to take moral/political accountability for how they might (consciously or unconsciously) be perpetuating those gender stereotypes. They shift onto others the ethical burdens of examination (by oneself and by third parties) and of change.
3. Generally, outside of parenting, physician-patient relationships, and other highly intimate encounters, no one knows anyone else's birth genitals. If you haven't known someone since they were a baby or medically examined them as an adult, you don't know what they looked like when they were born. So the notion that we should always publicly identify other people by their physical sex at birth is an unfollowable rule.
4. Why would it be necessary and fair, rather than limiting and oppressive, to announce an acquaintance's birth genitals (known or presumed) every time you refer to them? That is, why would you want to call people "he" or "she" for the sole purpose of repeatedly indicating your own belief about their genitals at birth? You might be incorrect, and, even if you guess correctly, it is intrusive to publicly air your presumption. Anti-trans cis people who are not arguing for jettisoning gendered pronouns (or similarly gendered speech and consciously gendered behavior) and who are arguing that these cultural behaviors are indeed necessary for identifying other people's birth genitals are making an enormous assumption that is also a bizarre one. Why should it be necessary for people to routinely make and reinforce assumptions about each other's birth genitals? If that's all that gendered speech does, that observation calls for dropping gendered speech altogether.
5. If anti-trans cis people don't believe there is any such thing as "feeling like" a man or a woman and if they intend to argue with any personal account that a trans person gives, then they shouldn't ask trans people to speak on that theme, since they are asking in bad faith. Assuming they don't take trans people or trans narratives seriously, then, if they wanted to avoid giving anyone a hard time, they could just say "gender is imaginary, let's not talk about fake things, end of discussion" and not bother asking trans people to divulge personal details or share personal opinions that they (the cis people asking the question) have no intention of listening to or seriously considering. Instead, they deliberately waste trans people's time. They ask trans people to justify their gender transitions and demand that trans people use the specific rhetorical method of narrating their gender feelings, and then the anti-trans cis people respond: Well, bad news: I don't believe that feelings can be gendered, and therefore there is no such thing as gender identity and no possible justification for gender transition. If that was always their position, they should not have fed the trans person a certain narrative framework they were "obligated" to use in their response and then, after the trans person complied, changed the parameters of debate and declared that any discussion of gender identity/feelings/behavior is meaningless.
There is no way to beat a troll at their own game if you follow their rules! You are fine as you are :)
