Safe Spaces are perfectly fine. (Some) men want some safe spaces, too - as there are things you just want to discuss with your equals (in gender). Why not?
The problems arise when everything in the world needs to become a safe space and at the same time everything needs to be inclusive.
Because then you start playing the “who-is-more-oppressed” game.
And that is a dangerous development.
E.g. Women’s only groups may exist, but a men’s only group might be seen as discriminatory.
But in the end when trans-fluid male identifying as women want to join the women’s only group they may, because else it would again be discriminatory.
But when a cis-women wants to join a trans-gendered group she might not be welcome, however when its a POC-women, she might, because else it would again be discriminatory against POC or maybe it would not be.
And that could be the end result when groups are seen the same as personal identities.
My own solution would be:
Let everyone define for non-public groups who you want to have as a member or not.
Women’s only groups are as fine as trans-only groups are as fine as men’s only groups are as fine as POC-only groups are as fine as mixed groups of any kind.
So let everyone have their safe spaces for themselves and define them as they want, but do not impose those safe spaces on the rest of the world as “the only way to see things”. (Trigger warnings that can psychologically proven trigger PTSD could be okay for certain things IMHO, but there is also a certain personal responsibility for that. E.g. I would propose a web page where you can see if a movie or book contains things you could be triggered by.)