Free speech outlined in the Constitution is constrained by how loud you can shout. Groups like the alt-right are fueled, in part, because of the belief that they are subjected to unfair and targeted censorship on platforms like Reddit. If they are not able to participate in the discussions being had there, other groups are able to control the narrative to the alt-right's detriment.
Being able to defend yourself with your voice is a moot point because, in the age of the Internet, that is not where the discussions are taking place.
danjoc said that freedom of speech is only for those who own the press. zdw replied and said Reddit is privately owned and can do whatever they want. I presume that danjoc interpreted "privately owned" as an instance of "those who own the press", which does not seem to be a stretch at all.
Being able to defend yourself with your voice is a moot point because, in the age of the Internet, that is not where the discussions are taking place.