This question requires a bit of background to what initially triggered this whole mess, as the reason those terms get brought up a lot is heavily intertwined with the history of Gamergate and their opposition.

Whether or not some parts of the GameGate crowd want to acknowledge it or not, it really began to take off when it came to light when a small-time Indie developer was found to be sexually involved with some gaming journalism folks who had also given exposure to her game. Lots of other evidence of some rather unprofessional conduct began to crop up. Many of these folks were well-known members of the online "Social Justice Warrior" clique.

Anita Sarkeesian, at the time, was probably one of the most well-recognized members of this clique. She was already unpopular in many gaming circles because she was viewed as an outsider attempting to make a quick buck off of criticism of the gaming scene, rather than a long time gaming supporter who was attempting to bring something new to the table. Often her lectures would highlight what gaming was doing wrong, but very rarely what it was doing right or what it could be done to improve. She then did a Patron or Kickstarter (can't remember which) which most think she has now under delivered on, feeding that idea of someone who is just leeching off the industry for a quick buck. Note, she was still relatively small peanuts at this time.

Back to the brewing scandal, this clique, rather than acknowledge that the behavior of these individuals was unprofessional of journalists, instead began pulling strings to attempt to blackout the discussion and when that failed, to try to portray their detractors as misogynistic, racists, or what have you. This was an attempt to once again stifle discussion, by using modern society's tendency towards political correctness.

This is how the idea of Social Justice Warriors, got brought into the scene. These folks are not a single mass, as many like to present. They range from the barely involved who support the idea of social equality, but don't really look into the sources or background of the people they are getting their information from, all the way to people who may be actively malicious and attempting to use a crowd of would-be do-gooders for personal profit.

Gamergate folks generally get exposed to the most extreme segments of this population, with the weight of the less radical/informed masses behind them. These folks are a strange bunch. In their pursuit of "equality", they often propose horribly sexist or racist policies themselves. Either by attempting to "turn the tables" on the old oppressors, or just willfully ignorant ideas like trying to fight "cultural appropriation" by segmenting off that section of society, without failing to recognize that's just plain racial segregation. They tend to get mocked because they're viewed as a bunch of people with really fringe ideas who use their more moderate supporters to attempt to impose their will on others.

Feminism is another strange "target" in this, because in the classical definition, many GamerGate supporters are feminists. The idea that people should have equality before the law is not that controversial. What has become controversial is the specific brand of feminism that SJW typically tend to advocate for, which is that the feelings of the most easily offended outweigh the right for others to express other opinions.

Most here have no issues with women in games and gaming, but also aren't going to bend-over backwards for someone who isn't willing to put something forward. Put up or shut up as it were. That's part of why you saw such a great reaction to The Fine Young Capitalist's kickstarter campaign. These folks wanted to get women more involved with games and gaming, and they did it by going out and creating a way to bring girls into the scene, rather than by attempting to pull down and criticize the content of others.

What I believe many around here would say that feminism's most vocal leadership are beginning to become a parody of the original movement. That many of them stopped being about equality between the sexes and started becoming about supremacy of the former underclass or an attempt to drag everyone down to the level of the lowest person in society.