I've seen this stuff pop up a couple times and I always want to contribute, but I'm not sure how. As this is a discussion, maybe now is the best time to take a shot.
First, I'll say: Ladies, men, and anyone who identifies by anything else, if someone offends you - especially someone you know or spend time around more regularly - please let them know. Hopefully they will take it in stride an do their best to censor themselves around you. Eventually this would become second nature and start carrying over into other areas of their life. Then you reach the point where the offensive behavior is instinct and the person can instinctively pass it on to their children and, in the long run, help eliminate something.
Even if it doesn't go that far, knowing is half of the battle. If something doesn't compute as offensive for me, I won't realize that it is for someone else. Which ties into my next point, the discussion bit.
Regarding the OP (part 1), that is messed up. Maybe I don't pay attention enough since I haven't seen things as bad as you mention. But what you've experienced is not something that should ever be the case. I'm ashamed that it happens on GoIO enough for you to even have to post here.
Regarding the OP (part 2) and Andika's post, that is equally messed up, but I can delve a little deeper in to that.
Concept-wise, the idea of an exclusive group grates against what it is to be a social human. If you say you have a group and I can't participate, it bothers me, whether it is something I even need to be in or not. Conceptually I would feel mollified if there was an alternative group that was equally exclusive in the opposite direction.
Conceptually, there are no male exclusive groups. There are no male exclusive events. Your average guy, upon seeing a female exclusive event, would feel insulted. Certainly no reason to make a scene, but why are you being excluded? You are nice to people. You don't do or say anything offensive. Some of your female friends are going to be in it. But you can't.
Realistically you also have to look at the female perspective, and actually comprehend. Go in to a lobby and try to make a group. If you are successful, odds are you just made a male-exclusive group. You didn't try to. If a female was there you would have taken her too. But they weren't. Now imagine you are female looking for a group (and correct me if/when I'm wrong, please). Every group is inherently almost male exclusive. Not in name. Not in rule. But here you are trying to break in on the guy's club. Are you really welcome? Are you really welcomed, or just tolerated because female?
Genders do exist, and are especially noticeable in video games which are so predominately male. It is inevitable that a statistically significant percentage of females to play may at some point find the pre-existing groups to be equivalent to male-exclusive. In this light, making a female-exclusive group makes sense for relief. Explicitly making it exclusive makes sense. But it clashes with the male perspective that the male groups are not exclusive, so a female exclusive group seems like nonsense to some guys.
Long story short, guys don't understand the need for the group, and don't understand that they don't understand. Shame on us.
In the larger context, getting in to the ideas of yes-all-women and not-all-men, and the way men treat women in casual encounters in person and online.
From the male perspective. I feel safe walking alone. I never get random compliments on my appearance from strangers, but I would enjoy them. I am not a small man, and I'm pretty confident that if attacked I could probably fend off an attacker even without training. I never feel threatened.
"You complain about being complimented by strangers? What??"
From my perception of the female perspective from speaking with friends (please please please take this with a grain of salt. May be dramatized since I don't actually know). In general statistical terms, women are weaker/smaller than men physically. You are told stories from the news, the internet, from friends and family about attacks, sexual assault, rape, etc. Walking alone, the person giving you a smile and a compliment while passing by could be friendly, or could be wondering how best to get you alone. In person and online, comments could be either kind or threatening. You want to give someone the benefit of the doubt, but if you are wrong, it costs you so much.
"Of course I complain about getting complimented by strangers."
For guys, imagine that everyone has a gun - except you. People on the street. People in your work office. People online. Everyone. But you don't. Everyone else carries this around with them. Maybe they never use it in their life. But they could. Everyone always has this power except for you. And everyone knows it. Someone smiles at you on the street. Is that a friendly smile or a threatening smile? Someone actively threatens to shoot you. When can you feel safe? You can't live a life in fear. But you also can't be stupid. You go home to have some fun time online, but everyone there has guns. If you let them know you don't have one, everyone makes fun of you and threatens you. You try to make a group only for a few people you've met without guns and everyone with a gun gets up in arms (get it?) about being excluded.
Does that start to make sense?
I don't have an answer. Here or in the world as a bigger place. Girls, I'm sorry. Guys, acknowledge and try to understand.
We can't control anyone but ourselves, and if we aren't around when bad things happen we can't help that either. But we can do our best to be observant when we are around and defend what is right.
TL;DR: Guys, we don't even understand how much we don't understand. Read my analogy. Find a girl and talk to them about it with absolutely no condescending or insulting treatment of the girl who tries to explain.
Girls, we don't even realize how much we don't understand. It isn't an excuse, but if a guy asks you to explain and you can, please try to help us understand better.