One of the most destructive weapons of Identity Politics Ideologues is the policy of attempting to get dissenting voices De-Platformed, or to have the ability of them to speak removed. It is this aspect, perhaps above all others, that renders Social Justice as a whole hostile to online discussion and discourse. By attacking the ability of dissenting voices to have a platform, Social Justice Warriors establish echo chambers and attempt to remove dissenting opinions.
The process of De-Platforming, alongside Safe Spaces, is devastating to online discourse for several reasons.
De-Platforming Encourages Extremism
Bad ideas normally perish on the altar of public discussion; it is very difficult, for example, for someone to argue that we need to be openly racist without supporting justifications in a public discussion forum where anyone can talk about it. The ability of the common person to look at and see why it's a bad idea is necessary to helping to prevent the spread of such ideas.
But by actively attacking the ability of a racist to talk about it (denying them a platform), however, this behavior encourages a "forbidden fruit" paradigm where "undesirable" speech can fester in locations where it cannot be covered, resulting in it going unchallenged for some time. By the time it emerges again, it has managed to fester into extremism, where it is far more destructive than it would otherwise be.