If we grant that the definition of dissent in the political context is the holding of a belief that is contrary to the prevailing ideology, then it’s not particularly difficult to categorize instances of such dissent.
A good metric to measure it by is the magnitude of social penalties paid for by expressing potentially dissident beliefs. Can you lose your position at a company that you yourself started over the beliefs that you express? You are probably engaging in genuine dissent. This happened to Brendan Eich at Mozilla when he donated $1,000 to an advocacy organization that had Barack Obama’s 2008 opinion on traditional marriage. Something similar happened to Pax Dickinson for making crude and heterodox tweets about women in tech.
However crude the boundaries are, it should be easy to see what cannot belong in the category. It’s hard to think of a situation where holding left-wing beliefs, no matter how left wing they are, would get someone removed from an an organization that is not itself expressly right-wing.
I can, however, think of examples where lefties didn’t get shitcanned. In 2001, Ward Churchill, a UC Boulder professor, literally argued that financial killed in the 9/11 attacks had it coming. Adam Kotsko, another academic, had similar sentiments about the Charlie Hebdo attacks: the people at the newspaper were insensitive to Muslims and therefore deserved to die.
“Can it get you fired?” is by no means a necessary element when looking to categorize something as dissent, but it’s a pretty good barometer for the climate of official ideology; that is, the underpinnings of polite culture that we’re expected believe. Both of these men, of course, made waves. There was a lot of outcry, and Kotsko eventually deleted his Twitter account, but neither of them suffered real material setbacks.
Indeed, the official ideology is not really democratic: right-wingers get fired for expressing even mainstream opinions, left-wingers do no get fired for expressing universally revolting opinions. Most American’s probably do not want gay marriage, but that belief system doesn’t use the ideological assumptions that it is supposed to. Churchill’s 9/11 apologia was underpinned by the belief that there is Wall Street imperialism in the third world and that it is bad. This is firmly in line with with the ideological assumptions of powerful cultural institutions. So is Kotsko’s belief that racism is an insurmountable evil.
The pseudo-dissent that leftists engage in is merely a demand to extend official ideology and praxis. If we’re sitting somewhere around 6 on the Official Ideology Scale, the supposed dissent of the left is just a petition to crank it up to 11.
The FBI officially makes it its business to infiltrate and disrupt white supremacist organizations, and fashionable Black Lives Matter types like Ta-Nehisi Coates are also in the business of trying to dismantle white supremacy. There’s a difference, of course, of where exactly they think borders of white supremacist ideology starts and ends, but this is a question of magnitude, not a question of principles.
Black Lives Matter is a particularly pertinent example because such activists are supposedly fighting against “systemic racism” that is working around the clock to destroy them. The veiled is pulled back when we actually look at the casualness of these protests. There are no long-term legal consequences for anyone hunting for the white supremacist witch, much less social penalties. If anything, you can gain social credit by bragging to your middle-class friends about being on, like, the Right Side of History.