More specifically, by exploiting and weaponizing the good nature of others. This is why they went after geek hobbies specifically: science fiction, open source, comics, cartoons, video games, and tabletop RPGs -- because geeks are sensitive and accommodating, and shouting at them how racist and sexist they are is bound to make them stop and reflect -- leaving them wide open to further attack. Had they chosen to attack pastimes rife with actual racists and sexists -- tailgate parties in rural Georgia, say -- they'd be routed, because racists and sexists don't have the fucks to give about their behavior.
As I've said elsewhere, "SJWs" aren't really geeks. They are more like mentally deranged normies who long to sit at the cool kids' table, but don't stand a chance of ever sitting there, so they take over the geeks' table, because better to rule in hell than serve in heaven.
What we got was also predictable, though. If anyone can fight under any banner, if nobody owns the banner, there is no possibility to come to a compromise, to settle the differences. The proponents of a movement will pick the most benign shard as an example to defend and popularize their cause; the opponents of the movement will pick the most extremist shard as a justification to fight back. Everyone feels their survival is at stake.
It seems then we are not in disagreement over substantive matters, but over minor questions such as phrasing.
Even the "Black Lives Matter" movement is distracted from the goal of making black lives matter with a laundry list of progressive demands like dismantling the "Western-prescribed nuclear family structure" that are tangentially related at best. (Indeed, the entire premise of contemporary intersectionality demands one surrender the possibility of delivering meaningful reform on an incremental basis, in service of forming a bloc dedicated to seizing power wholesale.)