I can understand your viewpoint - on some levels, there shouldn't be any need for this sort of thing. Having said that, things aren't equal, and there is discrimination, and things aren't likely to become equal if you don't confront that.
We've had a women's group for some years, but I got involved a couple of years back because I had been wondering about why there aren't more women in my field (IT), given it's fairly well-paid, fairly flexible, can be interesting, always something new to learn and so on. I still don't get it on many levels, but I figured just thinking it wasn't going to change things, but getting involved could - so now I'm actively involved (not least because my useless manager initially tried to ban me from getting involved.) There are other groups - LGBT, some groups for particular ethnic/cultural groups, a green group and so on.
I've got so much out of it - we've been involved in things like working with HR in looking at where the women are in the company. We know the overall figures, but now we've got a much clearer idea of which departments are giving a good showing or not on equality. We've had some inspirational people giving talks, from high up in the company, as well as some external people. Plus I've been involved in organising things which is experience I wouldn't be able to get in my daily job. There's also community involvement - careers talks at local schools and so on. I've got to meet people all over the company, which is something which doesn't happen as part of my daily job - and it helps my daily job, as I get to know some of my users and I've made contacts with people at all levels, and met some really inspiring people - as well as making me more visible to others in the business, which improves my chances of promotion or can help if I go for an internal job.
We are involved in things like parental leave, and mentoring, and development. It is a way of improving things for everyone, not just the women, although the overall aim is to attract and retain women and support them.
As I said in my mid-year review to my manager, one reason I'm enthusiastic about it is because I get support, appreciation and can achieve things - it's something I tend not to get from my daily job. I've been able to take part in development programmes and workshops and so on and I hear about more things going on in the company as a whole - all things I wouldn't know about in my daily job without being involved in the women's group. My whole department benefits, because I pass on the things I hear about HR initiatives and new training schemes and so on. And men can join as well - we've got men among the membership, and at least one committee member.
It's made me far more positive about my employer - if I looked only at the company through departmental eyes, I would advise people to keep well away, if they were thinking of applying. The company I see through the women's group - which is far wider than my department - is one I would definitely recommend people apply to. It makes me feel involved and appreciated and as if I can make a difference. If it's well run, it can be a really positive force for everyone, not just the women.
(And there's the enthusiasm of a convert...)