Actually I do think there does need to be some gatekeeping, yes.
I'm not saying you personally need to do it.
But people can't just go round redefining words that other people use to refer to themselves and expect everyone else to be OK with it.
If people who have penises, or people who shag people with penises, start calling themselves lesbians, actual lesbians no longer have a word to describe themselves.
If male people, or female people who self describe as "cis women" change the definition of the word "women" to include male people, there is no longer a word that means "female people".
And it doesn't even stop there, because on this very thread we have someone saying that trans women are not male, meaning that even the words male and female have lost all meaning and we no longer have words to describe biological sex in humans. We can identify the different biological sexes in all other animal and plant species, but not in humans, because doing so offends some people.
Do you genuinely not see how this is problematic?