Let me try to explain what it's like, in a context you may relate to better:
Imagine you have a science blog. You spend all of your time critiquing and poking fun at anti-science ideas, and your followers love those posts. But you're also an atheist, and occasionally you blog about that too. First you make little posts about religion that have nothing to do with science - and while a couple people may get upset or use already refuted arguments, you're able to reply to them and explain the situation patiently.Replace "science" with "atheism" and "atheism" with "feminism," and you have me.
This goes on for quite some time, and more and more people start emailing you saying that while they didn't understand in the beginning, they now totally get where you're coming from - and some even agree with you! It's rewarding to know that your patience paid off, especially when that patience isn't always found at blogs explicitly devoted to atheism, which sometimes eviscerate and belittle any pro-religion argument.
But then one day you decide to write a post about the intersection of science and religion. Now many of your readers feel personally hurt. But to make matters worse, your blog post suddenly becomes very popular - now you have hundreds of people commenting on your blog, using the same old tropes that have been debated and debunked a million times before.
And since there's just not enough time in the day to respond to every comment (you do have a job, after all), you may make a general post about how all of their arguments are the same old crap. Maybe "same old crap" isn't the best phrase to use, because it incites them more. They start saying you just have a vendetta against religious people, and obviously have no rational responses to their arguments, otherwise you would have spent all day replying to them.
But really, you're just human. You're frustrated that you've spent years slowly educating people about a topic, but when you turn the spotlight on your own group, you realize you have so much work to do. And really, many atheist bloggers say you're not strident enough - if people get this upset by you, what would happen if they visited an exclusively atheist blog? You have many friends - also bloggers or important people in science - saying they totally agree or sympathize with your post, but they don't publicly say so for fear of also facing the wrath of these people. You feel alone in what you consider an important battle, facing an endlessly respawning horde.
So yes. When I read comments on posts about feminism or sexism, sometimes I lose my cool - because a cause that seems very important to me now seems hopeless. Because tropes like "you're being irrational," "you have no sense of humor," "you're overreacting," "most people didn't have a problem with it," "why don't you worry about things that matter," and "you have an agenda" have been historically used to silence women's voices from political issues like voting and birth control, to pointing out sexism on blogs and twitter. Hearing them is like hearing someone assert "But I didn't evolve from a monkey!" for the billionth time.
It's hard to remind myself that many of you don't realize that those are tropes and that they're so triggering to a feminist. I know I need to be more patient sometimes, but I'm human. Maybe you still won't agree with me about what I consider sexism or my views on feminism, but hopefully you'll understand why I get so upset when I realize my uphill battle is more like scaling Mt. Everest without climbing gear.