Anyone who is familiar with Batman knows this is a reference to The Killing Joke. In that comic the Joker shoots Barbara Gordon, paralyzing her, and takes naked photos over her to send to Commissioner Gordon to torment him. It's pretty f**ked up stuff. But it was the 80s, it was Alan Moore, and there were probably drugs involved.
The outrage over this can be summed up in a few statements.
"This shows a powerful character in a submissive pose because she's a woman! No male superhero would be shown in such a vulnerable pose."
An excellent point. I totally agree. To highlight this point some artists have responded to this by drawing male characters in a similar pose. It doesn't work. Your brain rebels and goes "Superman would never be so vulnerable!"
"This doesn't at all fit with the tone of the current Batgirl comic!"
You may recall that Babs became a hipster, moved to the "trendy part of Gotham", and now spends her time solving the problems of people who have the means to solve the problems themselves (i.e. rich/white people whom the cops eagerly would assist). She also has anonymous, regrettable sex, the way that strong female characters do. Keep in mind; a few blocks away Bruce Wayne is taking down mass murdering psychopaths who prey on the poor and vulnerable. Batgirl is such a hero!!!
So in this hipster version of Batgirl she was never shot by the Joker, stripped naked, and humiliated, right?
WRONG. That all happened. They've brought it up in the current continuity.
If anything the tone of the current Batgirl stories don't fit with the history of her character. The problem here isn't DC bringing up this event AGAIN, it's that the event happened at all. If you want Barbara Gordon to just be "another girl" out there having fun; ret-con out the part where she's nearly murdered and possibly raped by a serial killer.
"Male heroes aren't defined by a trauma the way that Batgirl is."
Yeah, that's a good--wait, no, seriously, did someone make that argument?
The Real Problems With This Controversial Batgirl Cover -- From io9
Yes, yes someone did. I mean off the top of my head I can only think of a handful of male heroes defined by a traumatic event. But they're all pretty minor characters you've never heard of. I'll list a few, but bear in mind I'm not an expert.
There is a guy called Bruce Wayne who watched his parents be murdered before his eyes. Now he's a totally messed up vigilante who dresses like a bat and can't hold personal relationships with any human beings except the boys that he puts in harms way as his sidekick... and his butler.
There is a guy called Peter Parker who watched his uncle die right before his eyes... oh and the love of his life was also killed when one of his nemesis made him choose between her or a bus load of people.
There's a guy called Ben Grimm who was transformed into a horrible rock monster...
There's a guy called Logan who was experimented on by the government...
Thre's a guy called Tony Stark who was held captive by the North Vietna--Afgan Rebels...
There's a guy called Frank Castle...
There's a guy called Erik Lehnsherr...
The list goes ON and ON and ON. For every Thor, who is just some mighty being punching villains just because, there are ten characters who do what they do because of some horrible thing that happened to them.
The cover is in poor taste. Hell the original comic was in poor taste! So much so Alan Moore regrets writing that bit. The real shame isn't on DC for re-creating that moment in a variant cover it's for keeping it in continuity and acting like it didn't happen.
People need to understand though that traumatic events are part of the comic mythos. They have been for a long time. It would be ludicrous to think that female characters shouldn't (or can't) bear the same burdens as their male counterparts. Now, should those traumatic events be things that would be totally absurd happening to a male character (i.e. stripping him naked and sending photos to his parent)? No. But bad shit will happen. It just needs to be in a more reasoned light.