To begin this, I want to say that I am generally critical of mass society for reasons detailed in both the Wikipedia and Meriam-Webster definitions posted in the question. If those two, taken together aren’t an argument against mass-societies compatibility with anarchic relations, I don’t know what is. Instead, I want to focus on what makes mass society conducive to anarchic relations, and then maybe circle back to some criticism on the back end.
Mass society can foster anarchic relations in that it detethers individuals from place. Industrial civilization and all of its wonderous splendors (internet, jetliners, cellphones, highways, etc) allow a person to uproot themselves and transplant themselves elsewhere in a way that humans have been largely unable to do for 99% of our existence. This allows for the possibility of individuals from disparate backgrounds but who share affinities to find each other and carve out new spaces where they might more live out their desires.
For all of the ways in which we (anti-civ/green) anarchists tend to talk up small scale forms of human organization (bands, tribes), these small societies can become insular, and cultural mores (for example around gender roles, ritual/religion, intergenerational relations) can become deeply entrenched, and while there is perhaps no written law, there are customs and taboos which can circumscribe the autonomy of individual members to express themselves fully without facing ostracization. Without access to a wider array of options, one orders whatever is on the menu, without realizing that in addition to salmon and huckleberries there are also mussels and nettle greens. As some friends like to say, “yes, and…”
Mass society allows for anarchists to more easily and widely disperse their message. As to the efficacy of this, I am suspicious, but at least theoretically, if we view our ideas as one of many contagions, mass society permits these contagions, whether ebola or anarchy, to spread. Of course, mass society will also try to leverage its wealth of resources in ways that contain the spread of contagions detrimental to its own smooth functioning.
While I am opposed to efforts to make anarchy an evangelical project, I am interested in seeing the what A.G Schwarz refers to as “signals of disorder” increasing in frequency and impact, that, to sound like an insurrect-bro for a minute, moments of rupture become increasingly diffuse. Mass society offers particular advantages to this ranging from pop culture, and our ability to influence aesthetics of such, to social mores and the opportunities to spread new or more liberatory modes of interacting. I desire these things not because I want other people to be like me, or see things my way, but because the more spaces that operate or are informed by more anarchic relations the more I can exist on terms that I would prefer, both in depth and temporally.
Those are some of the possible benefits of mass society to anarchist projects, but on the other hand, mass society has always had a certain gravity to it that constantly pulls things towards the center, towards homogeneity. It is the cultural melting pot we were taught about in school, it is the caution to not say something to far outside of what people already believe for fear of alienating them. It is millions of people marching in pink hats as a symbolic representation of some degree of disagreement with the state of things. It is choosing to vote because it might slightly slow the increasing spread of authoritarianism, or half-mitigate the more reactive elements of mass society itself. Mass society is the melting ice caps that are the cost of our ability to more widely travel and communicate. It is the toxic waste from a medical industry that is allowed to continue because it at least temporarily eases the suffering of those in dis-ease.
Mass society might have some arguable benefits to anarchy, but I am still opposed.