@noeffingidea
You were so right with "People nowadays seem to have a hard time accepting that we are simply animals, mammals" and then you went off track a little.
As animals, we have certain innate traits and these are typically male and female. There are the numerous observed and proven physical differences; we have different skin, bones, muscles, organs, eyes, hair and brains. We have different amounts of different hormones. The brains fire differently and have different sized parts. All of this is down to biology.
However, the very suggestion that there can possibly be anything different mentally between men and women gets a certain type of woman quite het up. "that must be social conditioning. A construct of the patriarchy". That seems arrogant and forgetting the 'we're fucking animals' outlook.
It is not 200,000 years of social conditioning which means women are developed to nurture whilst men protect and hunt and build. It's evolution. We have different brains and they work differently. As this is where you're 'you-ness' / 'soul' / 'personality' / 'person' is, why shouldn't it be that a brain which would typically and usually be found in the opposite sex ie. the person is trans.
There's a reason boys and girls, men and women generally conform to stereotypes! Because the sexes tend to act and behave differently and that's because we are physically and mentally different. Assuming that we are equal in every way is arrogant and forgetting that we're fucking animals.
A trite example of women in STEM is still a good one. Fewer women in STEM even in very sexually-equal societies? The gender-deniers talk about hidden pressures, social constructs and whatever unprovable theories they can muster. Often they go completely silent. A very good theory for explaining this inequality is due to brain differences. Another fascinating difference is ASD - either a diagnosis split or a split in those with these disorders.
So, you can take the, to my mind, totally illogical and improbable standpoint that despite all the physical differences between the sexes, there are no mental differences, that any difference in behavior is because of society and that there is no such thing as a male or female personality or you think that with the massive list of provable differences, there are also likely differences in thinking and personalities and that you can be a woman in a man's body.
Defining 'woman' as having a vagina is simplistic and serves little purpose. The 'terf and proud' people (and I assume you're one OP or why bother with this thread) like to act as though men are a class and trans women are under cover agents / spies for the patriarchy in the big conspiracy to get our Top Shop changing rooms.
You're in the minority though. Most of us don't care. We don't fear men and screw up our faces at the 'erosion of womanhood' nonsense.
@littlemissrain - I thought that feminism was not a homogeneous blob with thought police and group think. Why can't they have a different definition of feminism to yours?
My definition of feminism is likely different to yours.