I'm in the USA, and I attend a Ukrainian parish...and we are NOT segregated.
We used to be, with women standing on the left as you enter, and men on the right.
However, over the years many young families have joined, and the parents wish to tend to their young children together.
Today, we stand wherever we like.
I am witnessing this transition occurring in an Indian parish and it makes me sad.
I can think up possible reasons, but rather than presume... why do you feel that way?
I keep forgetting about this thread because of where it's located. Apologies.
I prefer the original arrangement ("gender segregated", to use the terms of the OP) for a few reasons which I'll throw out there in no particular order with the disclaimer that I haven't really thought about them so thoroughly as to write about them more cogently.
One reason is simply "tradition". Until very recently in Christian history, all Christians arranged themselves in this way during communal worship and did so from as far back as we have records. This tradition transcended language, culture, geography, denominational boundaries, and just about any other dividing factor we can think of. Because of the high regard we have for received traditions, this is enough of a reason to keep it.
Segregated arrangements are less distracting. No matter how much we try to focus on our own response to distractions rather than the things/people we find distracting, it is helpful to limit distractions as much as we can. Most people will read that and think I'm talking about men gawking at women and vice versa, and that's part of it, but it's not by any means all of it (and anyway, if you, like my cousin once upon a time, are determined to gawk, you'll find a way to stand through a three hour Liturgy with your head peering over one or the other shoulder and not care that dozens of fathers-of-daughters can see you).
I think the segregated arrangement is a sign that speaks more loudly than any sermon could of our creation in God's image and likeness as male and female, about the inherent goodness of sexual difference and the dignity of men and women as men and women, about how we approach God and are saved and sanctified precisely as men and women, etc., and it seems to me that we need to bear witness to that teaching today more than ever.
Related to this, I think it's helpful in modeling the faith for future generations. Young men and boys standing on the men's side of a church are surrounded by and observe older men while they pray and worship, are perhaps even guided by these men in how to conduct themselves during the services, etc. They learn how to be Christian men by spending time with Christian men. The same can be said for young women and girls worshiping in the midst of older women.
It seems to me that women have an easier time forming community among themselves than men do, but it's important for men as well, and I think segregation helps both men and women do that. A non-segregated church typically arranges itself along (nuclear) family lines first and then perhaps in proximity to other friends or friend-families. In a segregated church, it's just a bunch of men on one side and a bunch of women on the other. It's more difficult to see the relationships that have brought everyone to the same place (e.g., blood, marriage) and you are less limited by them, so you are free to forge new bonds. The church becomes "family" more radically than in mixed congregations.
When I wrote of my sadness at watching the transition from segregation to mixture in a particular Indian parish, it's primarily because the members who are most enthusiastic about the transition seem to view the things I've just described as outdated, irrelevant, obsolete, even perhaps bad. They seem to want a more personalised parish experience into which their family unit can plug in as a family unit
, preferring to maintain the independence of the nuclear family from the larger community. They'd probably view the appeal to tradition as a form of antiquarianism, and while they probably accept the traditional teaching on creation and sex, I wouldn't be surprised if there was a hearty "Yes, but..." lurking beneath the surface. Because this tradition has been lost even among many (most?) Orthodox in this country, it's easy to understand if our priests go along with their parishioners' request to implement mixed seating/standing and choose something else to fight for, but in doing so I think we will have lost something of great value.
I'm not saying that segregation is a panacea. Segregated parishes have all sorts of problems. But ultimately I think it is a more catholic way of standing together before God than the non-segregated arrangement, which seems to me to be more focused on family, tribe, and/or the individual.