Not everyone has been a gamer as long as others. For some, they got into it fairly early, in the late 70's (earlier if you got into D&D) and early 80's, like me. It was a fringe activity, and the people who played them were typified as loners, losers, nerdy, bookworms, and generally social outcasts. It was just generally not a good thing to be lumped into that group, with rare exception. As a consequence, however, the gaming community tended to be all-inclusive in its membership, and didn't judge a person beyond their love of games. It just didn't make sense to, since many of the first gamers knew what it was to be ostracized, or made fun of because of their hobby. After a while, games became a common link that overcame other differences, and was a neutral ground where disparate groups could put aside differences and focus on what brought them together, just like any other hobbyist.
Over time, and in many ways because of the advent of online games and gaming, the hobby evolved into something made more anonymous, since prior to online games, all games were basically done face-to-face, or at least side-by-side when it came to video games. It also happened to turn out that, initially, the majority of people that fell into the 'gaming' tag were males, typically because of a lot of the content of games being targeted at men and boys. This grew and was brought more and more into the mainstream, with shooters, online racing games, and topics that were, once again, stereotypically more appealing to males, rather than females. Things sort of crept up in the culture, and went from being an all-inclusive place to a 'boys only' club. Sub-cultures, like so-called bro-gamers, brought some of spill-over from other cultures, like sports, that typifies bonding via personal insults and machismo; nothing wrong with that, in it's place, mind you: hell, I do it all the time at work.
Unfortunately, a mash-up of a lot of these variables ended up creating this idea that women aren't welcome, or that if they want to be part of the gaming community, they need to put up with more bullshit, or that it's ok to objectify them. If you don't think it's a common problem, look at this (a lot of this is pretty painful, awful shit, so be warned: potential trigger warning, and please skip if you are even remotely emotionally sensitive):
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You get the idea.
This is not OK. (Big shout out to Fat, Ugly, or Slutty for doing the best thing you can for this shit: posting it, making fun of it, and taking away it's power). This is barely scratching the surface, and it gets so much worse.
Finally, we're getting to the most recent issues, which circle around a columnist and advocate named Anita Sarkeesian. Now, this woman is no stranger to controversy; her career right now is bringing to light a lot of the unspoken assumptions in games, game development, and gaming culture that tend to be either actively misogynistic, or just tend to gloss over women and their roles in those areas. For this 'crime', she has received regular harassing calls, threats of rape, death threats, and most recently has been forced to leave her home under fear of death.
This is not who we are.
There's been a lot of outreach on the subject, from fine individuals such as TotalBiscuit and the great people out there at Extra Credits, who made a much more eloquent video regarding the problem here
We were the one group everyone was welcome in, no matter what, so long as you loved the games. We need to be that again.