It's not that people don't understand why someone might find something offensive, it's that we don't give a shit. Most of us avoid what we find offensive and generally speaking don't feel the need to make waves when we come across something we could never like. We just move on. There's a series of adult comic books that feature the rape and mutilation of women. I find that very offensive, and don't buy them. Someone else goes for that, as long as it stays in the realm of fantasy, it's not my issue. Someone else see this on the other hand, and it becomes an issue. Some say they just want to have the conversation, but ultimately, the point of complaining is the hope that your complaint will be addressed. You say they don't want to take our games away, but if that were 100% true, they wouldn't be opening their mouths to say how wrong they think "sexist thing A" is. They do so in the hopes that "sexist thing A" will go away, something through censorship, and sometimes in the hope that you can, by complaining, bring others to be offended by what you're offended by so "sexist thing A" won't be in demand anymore.
I can't (without being a hypocrite) tell people not to complain about whatever grinds their gears, and it can be well justified and the best way to achieve and end goal, but we need to quit pretending that all the "isms haters" out there just want to talk and have the conversation. The conversation must have an end goal in mind, or else people are just raising issues to hear the sound of their own voice.
And I won't deny gamers can be a bit over-reactionary to someone bringing up issues. Face it, we've seen the whole medium get judge for violence by a few titles, or on sex by one cutscene from a game the pundants didn't even play. It's not hard to see any issue as overblown when somehow the medium can't have anything with sexism or racism within it, or the whole medium gets dragged through the mud for a few bad examples. That if we have the conversation all that will happen is a few incidents will become the indictment of the whole industry because to those complaining, they don't see the industry, only those games with impossible boobs and outfits, or the white character killing black cannon fodder. I'm not sure how to break through this, but a good step would be for those that wish to talk about video game sexism to come with numbers to the discussion. If we're going to have the discussion, let's talk about the industry, not a sampling that paints a picture based on Lolipop Chainsaw, not The walking Dead, Persona 4, Portal, Minecraft, Virtue's last reward, Ni No Kuni, pokemon, ....