For as long as people have been talking about social justice online, there have been people, trolls really, who make a point to argue, harass, and otherwise engage in actively hateful and bigoted behaviour. This has been the case in every online community I have been involved with: the feminist community, the atheist community, disability community. There is always someone prepared to defend the vilest behaviour you can think of. If you are a representative of these communities: a Person of Colour, a Trans Woman, a Disabled Person, if you are a member of some minority, the number of people who target you in particular escalates.
The sheer number of people committed to spreading hate has made places like the comment boards on Youtube a place to be avoided. Many magazines and blogsites have closed their comment sections. More than one writer, activist, organizer, and so forth has been forced off the internet as a result of death threats, threats of rape and violence, dealing with a constant barrage of slurs and hatred, and even having their private information released to the public.