I guess I'll just say what I always do to questions like this.
I like comics, but I don't think comic book fandom need only be about the things people like, but also a space for talking about what they don't like.
I think issues of social justice matter, that people should get mad about them, and I want comics to do better; but that doesn't mean I can't or don't enjoy stories about white, cis, straight men. I don't think "that's the way things are" is an excuse for marginalization, or a reason not to press for what you want to see in comics.
The only reason it seems like some fans are mad "all the time" is because they are willing to devote paragraphs and threads with detailed explanations as to why they are disappointed with the comic or the company. And frankly I am hearted by that, because these detailed explanations, to me, are a sign of a vested interest in comics; most people who complain, who devote their time to writing out detailed responses, are doing so because they really want comics to succeed. They are saying what they don't like, and by extension how comics could do better.
But people get uncomfortable when others are willing to voice their complaints, and suddenly it seems like "the haters" are taking over, when that is really not the case in the scheme of things. The written word is just the most common and accessible method for most people to discuss their disappointment. But plenty of us, even the people who devote paragraphs to our disappointment, also talk about the things we like in other ways; fan art, fan fiction, squeeing over movies. Tumblr is full of that stuff. The internet is full of that stuff.
In fact, I did quit comics because I was tired of what I was reading, and because they pulled the only things that interested me enough to buy. That doesn't mean I'm not interested in what is going on, or that I don't keep monitoring or hoping that something will come along soon enough to make me want to buy again.
Also, specific to DC Comics - if you pay attention you will note that the majority of people who are upset about the changes aren't mad about change itself; in my case, the idea of a reboot still sounds fantastic - but I am not overly thrilled with what they did. Most people are upset about what has come out of those changes, as in - "They could have done all of these things, but this is what they chose to do? How uninspired."
I love most of the characters in comics. The stories are hit or miss. But essentially I want good storytelling without cheap gimmicks or retcons - where writers can finish what they start - and where continuity has enough respect that I don't have to worry whether or not the next time I pick up a Batman comic he's a hero or an a*****e. I want fresh writers and fresh artists, and the opportunity for less iconic characters to play larger roles and have awesome adventures (not just the same 10 people). I want to open a comic book and think, "Wow, this is a masterpiece."
Right now, comics aren't offering me all of those things, or even a significant portion. So I feel like saying why and hoping someone will do something about it.