I'm not seeing those arguments. Whose argument are you referring to?

Despite being a strong privacy advocate, I didn't find the post particularly compelling. For the vast majority of open source projects, discussion of anything illegal would be considered off topic, and there is no expectation of privacy since all discussion is public record. Having those discussions being public and searchable is a valuable feature.

Does that mean I am against good tools that enable private discourse (like Signal)? Of course not! Some open source projects probably have a need for private discussion channels. I'm all for them using them. But to then extrapolate from that: "don't use Discord to discuss your open source JS widget library" doesn't make sense to me.