The solution to a social problem can be social in nature.
If you apply this to the OP blog post you can see that the desire to get away from IRC to "safer" products comes from the desire to deal with the social problem in a social way, but in a hidden way:
The technical solution will supposedely make it easier to apply the social solutions, i.e. the barrier of entry for undesired participants will be higher.
An undesired participant can be someone who questions Mozilla on a fundamental level (i.e. on the topic of meritocracy, privacy, inclusion, activism, etc.)
The proposed solution is reverting to a "safe space", i.e. something that promises to automatically protect against undesired participants, because Mozilla has long ago decided that it does not tolerate being questioned on a fundamental level.
This ultimately results in a reclusive filter bubble, where a significant part of the audience is no longer allowed to exist.
Since Mozilla does not seem to want to invest in moderating these spaces in a democratic and open way, which is very costly (but human relationships are always costly), the proposed solution is to build a fence between "us" und "them".
