As soon as you start identifying as a man, you are expected to shed away anything that alludes to any kind of womanhood you might have had previously (or currently, for that matter). Even "progressive" types will balk at the idea of a feminine man or a man with any ties to personal womanhood. Many people think that if you're in any way connected to womanhood that makes you less of a man, and none of those people seem to recognize or care that that is misogyny. This is especially true of trans men, whose manhood is constantly scrutinized & called into question no matter how hard we try. Some trans men respond to that expectation to be As Cis Passing As Possible and conform as best as they can because they are Afraid Of The Consequences or because they desire conformity, but many of us cannot or will not cut away parts of ourselves to fit into a ciscentric idealized version of manhood. It feels like most people expect you to want to perform Cis Manhood, and anything less than that is not Real Manhood. They cannot imagine that Trans Manhood is often purposefully different from Cis Manhood, and often challenges the attitudes around what men Can Be.
Too often you see, "Trans men are men," as a way to delegitimize our connection to certain histories or present-day oppression of women. Instead of extending the history & oppression of women to include trans men, the expectation is that trans men must not acknowledge our past or our present suffering. It's never, "trans men are men, so maybe we should open up these conversations to include them." We are expected to continually center cis women in issues of reproductive care, pregnancy, sexual assault, etc despite being some of the main victims of systemic oppression surrounding these topics. Culturally, forced pregnancy is not a "men's issue," but among trans men it is one of The Major Issues that regularly kills us or attempts to strip us of our manhood & put us in our place (so to speak). But the idea of including men in these discussions -- or even just not actively excluding men -- is ridiculed, dismissed, and ignored.
To be clear: these are not men's issues NOR women's issues. They are people's issues that happen across gender lines and (in the case of some intersex variations) sex lines. You could just as easily describe them as nonbinary issues or agender issues and remain just as accurate. Your ability to publicly claim them as your own issues & be taken seriously highly depends on whether you are willing to interact & talk about them entirely in a woman-centric way. For many trans people, that is dysphoric. And for those of us who are willing, it's pointed to as proof that we're not "really" trans.
We point to certain historical figures like Dr. James Barry or Lou Sullivan as proof that trans men existed, and those people are often ripped away from us and categorized as "historical women." (Proving that if even one thing is called into question about your manhood, you will be stripped of it -- especially if that thing is your own biology.) But the existence of trans men, historically, should not be in question. There have been trans people of all kinds for as long as there has been gender. You see echoes of it written all over personal accounts, in art & literature, in newspapers. Most trans men in history were not as lucky as Dr. James Barry or Lou Sullivan as far as ability to express their manhood goes. (Hell, even those guys didn't always have it "good.") Most trans men were murdered or punished or sent to mental institutes or forced to be wives and mothers or mutilated or lobotomized or thrown out in a time when they legally could not easily own their own money/property or could not get hired for substantial work, or did sex work and went to prison or died of venereal diseases. This is our history as much as it is the history of women, but only cis women get to claim it without having to challenge their identity.
This is what I'm talking about when I'm talking about transmasc erasure. You don't see these things as anything other than women's history, but we are right there in the margins. You can't come at me, a trans man, acting like I have no idea what women have been through historically, because I could have been any one of those women in the past. You just don't see the people like me in your history books outside of MAYBE one or two "strong historical women escaping gendered oppression of the time" and have somehow decided that it was lack of existence and not the much more obvious reality that trans men have always been forcibly categorized as women, forced to live as women, and systemically silenced by the strict gender roles of the patriarchy. Many of which still exist.
So when someone tells me to shut up and sit down and let the women speak about so-called women's issues, I wonder if they understand that they are doing nothing new or radical in trying to silence me or exclude me from those issues. I understand why perisex cis men might be expected to shut up and sit down when we're talking about pregnancy, but when you say it to me (again, a TRANS man), it's just transphobic. It's a way to force me back into womanhood OR a way to force me to suffer in Idealized Manly Silence. Either I'm allowed to have a voice and my manhood is questioned, or I'm not allowed to have a voice and my oppression goes unnoticed. And so people get mad when you can hold both truths at once: that I am a real man AND connected to so-called women's issues. Talking about my connection to those issues doesn't make me less of a man. Rather, they expose the deep transphobia of the ciscentric feminist framework we have.
And I think that is why trans manhood is so often punished/attacked from both sides of the gender conversation. The Patriarchy can't allow us to be real men because that upsets the idea that women are naturally submissive/weak/stupid/lesser/etc. Cis feminism can't allow us to be part of conversations about our issues because that would upset its marriage to oppositional sexism & the transphobic idea that by including us they must "center men" in what has *always* been considered "women's issues." They see our existence and our hunger to be included as an attack. They don't understand or care about how that's transphobic. Again, it comes back to "trans men are men and men have been centered for so long that it's time to focus on women" and ignores, "trans men are men, but they have been deeply ignored and silenced throughout history, so centering trans men is not the same as centering perisex cis men in feminist conversations."
I've largely framed this as a transmasculine/trans man issue because that is mostly how I experience it, but we are not the only ones this happens to. Trans women's womanhood is often challenged as they fight for their place in feminism due to their perceived proximity to men (the "centering men" thing is also used as a constant attack against including trans women even though they are literally women). Furthermore, the gender/sex binary is, perhaps, an even more exclusive and prevalent system of oppression that the patriarchy is built on and stems from. It is so normalized that even other trans people get mad when you bring up nonbinary identities or intersex variations that challenge their identities as men & women, female & male. I believe this is one direct cause as to why so many of us are gatekept from conversations that should include us.
My point is that ciscentric feminism does not make room for any of us & is actively failing all of us. Any transfeminism that is uncritically built on & mirrors ciscentric feminism will inevitably fail entire groups of trans people -- most likely the ones who challenge the system the most in their deviation from the binary norms expected of them. If feminism wants to be a movement for gender equality & sex liberation, it needs to be for everyone. And if it can't make room for everyone, then maybe it's incapable of achieving that future.