Whether private companies should not be able to discriminate speech based on content is still up to debate, but don’t compare this to shouting.
This is the sealion's argument, that you have to be willing to engage with them at all times in all contexts. It implicitly denies freedom of association. For example, if I am running doomermetalchats.com do I have to tolerate K-pop fanatics with their relentless positivity and sunny optimism?
The doomers and the stans can be talking right alongside each other and never see each other; effectively, the doomer 'site' only exists virtually, as a mutually visible consensus among a subset of the network.
There are a few different motivations for social communication, both cooperative and antagonistic. People often want to be able to communicate freely with their peers and exclude non-members of their peer group (socially, algorithmically, or by fiat), but sometimes also to be able to push into and perhaps take over network territory of rival groups or that they consider should be common.