1. The biggest straight-up error made in the activist left, I think, is the belief that nobody of any consequence changes her or his mind about policy or social practices by looking at which side has better epistemic hygiene. The formalist nerds are many, they are influential, and they hop real far across the spectrum case-by-case based on their judgements about which side is more intellectually honest, well-informed, and searching. (Which is partly their best second-order method for informed decision-making, partly an aesthetic-social preference about whose side they want to be on, but that’s like anything else). And if these formalists are easily prey to false positives, biasing their conception of epistemic hygiene to the tactics of the libertarian right, they are also irreproachably reliable in recognizing a good argument, including a good refutation of a meretricious argument, biasing them all the way back to the tactics of a left that’s doing its damn job.

2. Not so damn obviously wrong, but probably wrong, and accepted as a given, is the theory that anything proffered as leftist thought should only ever be critiqued for propagating failures of solidarity or failures of intersectionality, and every other way in which a text or theory or programme might be normatively or methodologically or empirically messed up, on one’s best judgement, should be passed upon in silence cause these other modes of failure don’t have consequences worth the social price of a critique.

3. Both of these theories are weird artifacts of being a community that operates by putting pressure on institutional policy-making on a case by case basis, but lives off a theoretical folklore evolved for literally revolutionary politics – like, the lead-up to the Russian revolution – wherein the consolidation and mobilization of a vanguard could be separated from, and chronologically prioritized over, the deliberation over policy, and where convincing the ideologically uncommitted of the value of an individual policy is basically worthless cause you’re only ever looking to recruit, not looking to negotiate. This theoretical folklore makes zero sense when what you actually do when you do radical left activism is pick a policy decision you want made or changed and try to get a lot of people to agree with you out loud. 

[Update, three years past: still true but incredibly irrelevant rn.]