They are a fan of free speech == unrestricted speech. Most larger ecosystems these days have a code of conduct, restricting some forms of expression if they are deemed detrimental to the community. Something that very much riles advocates of unrestricted speech. Often, having a code of conduct is conflated with social justice activism - a movement that is prominently lamented in US politics more so than Europe.
Note: I'm not interested in debating which side is right here, or if that conflating of positions makes sense. Just pointing out the likely origin of the "microcosm" comment.