Hey! How's it going? Welcome to FWR.
As a newbie you won't know this but there was a guy round here a while back used to make the exact same arguments. When I have time I'll post a link to some of his threads. It will save you a lot of time to read them first and see the counterarguments that have already been made so you can make new points that take them into account. Otherwise, all you'll get from this thread is those exact same arguments again. New for you maybe, but kind of a done deal for those of us with more knowledge of the topic.
In the meantime, here's some starting points for ya:
If being a "man" or a "woman" is a personal determination, why are woman-only (and to a lesser extent, man-only) spaces and protections necessary? What common experiences do they support? Indeed, why even have different groups in the first place? Would it not be better to do away with this division of identity altogether, or consider it a consumerist choice more akin to which football team one supports (for those that care)?
The offending, and especially sexual and violent offending, differences between men and women are stark. Are you suggesting men are people who knowingly identify themselves as more violent and sexually aggressive? If so, should identifying as a man not be a red flag in and of itself? Should we not be subjecting all people who identify as men to preventative therapy?
And finally,
Regardless of gender identity and self definition, and notwithstanding the small number of humans with visually ambiguous sex characteristics at birth, humans are undeniably a sexually (in the reproductive meaning if the word) dimorphic species: two non-overlappong sexes, with physical and reproductive differences between them. Bimodal distribution of other sex differentiatiors sure, but not of the core sex itself. And well over 99% of humans are accurately identified as one reproductive class or the other at birth, and their sex has both physical and social consequences for them.
In the case of those of us who are female (in the purely biological sense), this has been at some points in time, and still is in some places, as stark as legally defining us as property and denying us agency, autonomy and access to political, economic or cultural power , socially making us responsible for our own rapes, and so on. And even in societies where on paper these oppression no longer exist, nevertheless the social, cultural and structural mores formed under them persist and continue to disadvantage us relative to those born male.
So if, as you posit, self identity should be the measure of man or woman based simply on how one feels likes and dislikes align to social expectations of those words , surely those of us who are of the female biological sex and sufer the consequences have the right to also identity ourselves as a meaningful group because of our shared biology and history? To tell the stories of our physical and social experiences rooted in and coloured by that biology, and to politicise and organise ourselves and demand social, legal and political support to deal with the social and physical consequences of that biology?
And, given that to deny us this moral right is as unjustifiable as telling people they must not organise by race or sexuality to describe common experiences and where necessary fight against prejudice, is it not morally unjustifiable to deny us the name "woman" given that it was the name that has always referred to us, the name under which our oppression was enacted and justified, and the name that connects us to our history and makes sense of the challenges we face today?
The self identity underlying your concept of "woman" may be valid, but the use of that particular word, one that comes with millenia of the history of an oppressed people who have existed over the full diversity of human history and cultures and who actually have very little in common with the narrow set of personality traits you consider meaningfully "woman's", is not.