I think if you look at the world today, there are still definitely some issues with institutional sexism, but I do not think they are any more salient in technology than anywhere else. If anything, I'd say tech (at least in the UK) has a pro-female bias, because there are fewer women in the hiring pool, and so if you don't make a deliberate effort to keep your team balanced you'll end up with a sausage fest. In the case of GrantTree, that meant making a deliberate effort to advertise in places which are not predominantly male, and to tweak the wording of our job ads to make it clear that women are very welcome to apply.
Last but not least...
This is sexism by any definition, presumably perpetrated mostly or entirely accidentally, and not by "jerks".
You can be a jerk unconsciously. Surely, most people are - I don't think anyone actively wants to be a jerk. If you look inside your mind and you spot a belief, especially one that you've acted on, that "women can't be as good as men at X", where X is any kind of activity practiced by a large number of men and women, then there's a bit of a jerk in you.
There are differences between men and women, and some things men are naturally better at on average (for example, world-class competitive sports where the amount of testosterone in your blood simply makes a big difference in your ultimate performance), but no job I've ever seen advertised touches on anything quite so extreme. Even oil rig workers don't need to be world-class weight-lifting champions.
Everyone has some aspects of their mind that are "jerk-like". What makes someone not a jerk in the long term is the constant re-evaluation of otherwise accepted beliefs (usually handed down by their parents) in the face of new evidence.
Again, however, that's not at all specific to technology...
Then it's probably good for you to realize that Mad Men purposefully uses the construct of a fictional past to create a neutral stage for the exploration of contemporary issues with sexuality and power dynamics in modern culture.
Why they chose this stage, and why it became such a success, is because it's capable of touching this nerve in modern culture by having a story line that is just extreme enough to be able to say "thank God we're not like that anymore" but still recognizable enough to think "that's a bit like X from the office."
I think you're right that things have gotten much better. I'm in academic math, and I hear horror stories from 40 years ago. Women tell me that sexism is still a problem, but a substantially less severe one. And also, as you mention with regards to GrantTree, I know of several efforts in math to deliberately reach out to women, which seem to be paying dividends.
40 years from today, I hope all of us will agree that these discussions are no longer necessary.
I think that it's very difficult to 'look inside your head' and specifically call out individual beliefs you might have. Someone who thinks it's OK to use languate that objectifies women, or thinks its OK to call a woman a 'girl' instead of a woman (do you know any men who are called 'boy' by a co-worker?) doesn't think its OK necessarily because they believe women are lower than men on a power scale. They probably think it's okay to say that stuff because of the culture they were brought up in - the vast majority of people they know never told them that it was unacceptable.
If I make a joke about how some co-worker of ours might have gotten to her position through a sexual favor, and you don't take offense, that tells me that it's OK to make that kind of joke. If you don't show that it's unacceptable to use that kind of language, it makes it implicit that it's acceptable to use that kind of language.
This means that plenty of people can be jerks without knowing it and without being able to reflect and realize that they were being jerks without a societal change. If all of a sudden, everyone you knew told you it was unacceptable to use that kind of language, it would be unacceptable. You wouldn't use it any more. The next person you saw use that language would be a jerk, and if nobody told him that it was unacceptable, they would be 'a jerk without knowing it'.
In the same way, when you live for years in a society where it's OK to make jokes about, say, how black people are 'built' for physical labor, and nobody tells you that saying that kind of a thing is unacceptable, it becomes implicitly acceptable. This can happen even when there aren't institutional forces at play.
If one or two people out of ten tell you that it's unacceptable to use objectifying language about women, you'll probably still think it's acceptable, but that those one or two people are just really weird, or extreme, or something. Then THEY'RE the jerks, for 'not being able to take a joke', or something.
It's only when six, seven, eight out of ten of those people tell you that it's unacceptable that you'll start to actually think that it is unacceptable. We form our definitions of what is and is not acceptable every day through our language and behavior on an individual level.
Language like this perpetuates cultural power structures in our society that we label sexism as racism.
So, I think that 'being a jerk unconsciously' is a reflection of the society, not the individual. Sure, there are plenty of people who just don't get the message, or really ARE 'unconscious jerks'(bigots), but the majority of the people that may fall under that category are just following perceived societal norms.
We're not at the point where much of the hurtful, sexist language is unacceptable, but we're getting there, so we'll see people from all ends of the spectrum - people who 'get it' and actively call people out on sexist language, people who just use acceptable language themselves and don't see the societal perspective, people who believe that it's culturally acceptable to use that kind of language, and people who know that it's culturally unacceptable, but are actually bigots.