It is often observed that the left forms circular firing squads — incidents where internecine struggle does serious damage to the cause. When this issue comes up, the point is most frequently to blame some other individual or group for starting a circular firing squad. This view of the situation seems to presuppose that people just up and decide to form circular firing squads and could stop doing so simply by up and deciding not to.
Less frequent are analyses of the structural roots of the circular firing squad phenomenon. And it is a structural rather than personal issue. An honest appraisal of the history of radical politics in the modern world will indicate that the threat of a circular firing squad has always been in the air — from the Terror that arose in the wake of the French Revolution, up to the various “purges” that have been endemic in Communist regimes. From a certain perspective, of course, there is little ground for comparison between mass deportation to Gulags and blocking each other on Twitter, but it is not sheerly coincidental that people reach for the imagery of “purges” in the latter incidents.
In The Structure of World History, Karatani tries to account for this eternal recurrence of the purge. Essentially he claims that it stems from the attempt to carry out a radical revolution “in one country.” This minoritarian revolution is necessarily vulnerable to outside aggression and interference from the established powers. This happened in the wake of the French and Russian Revolutions, for instance, with the major world powers sending in literal ground troops. This outside interference is coupled with the real possibility of subversion from within, as counter-revolutionary elements persist and individuals attempt to take advantage of the revolutionary situation for their own selfish ends. At times, the two threats may literally overlap in the form of spies, etc. And more broadly, it really is the case that a minoritarian movement has less room for division and dissent — you need “all hands on deck” when you have so few hands.
Under those conditions, paranoia is virtually inevitable, leading to a violent acting-out using the means available — from violent state power to rude Facebook status updates. And the very nature of paranoia implies that the action will be disproportionate and wind up sweeping up innocent people with the real malefactors (and missing some real malefactors).
Now as Pynchon reminds us, just because you’re paranoid, it doesn’t mean they’re not really out to get you. Existing radical movements are all minoritarian by definition. The circular firing squad phenomenon does go too far, but it is responding to real facts. The state really does use violence and defamation to suppress radical movements. Activist groups really are infiltrated by police agents. And more mundanely, radical causes really are taken up by individuals with selfish motives (cf. the prominent “male feminist” Hugo Schwyzer) — or motives that appear mutually “selfish” from the perspective of other groups.
Fortunately for the victims of “purges,” often the only field where contemporary radicals can exercise effective power is within the movement itself. In more loosely affiliated radical circles, the only means of exercising power is discursively.
The purge phenomenon does not necessarily lead directly to a decline in power of the radical movement. From a certain perspective, the Soviet Union was at its most powerful precisely when Stalin was most destructively paranoid. Such moves can signal seriousness and determination and inspire fear in potential dissenters — as we can see in the takeover of the Republican Party by self-styled right-wing “radicals.” In the end, however, purges lead to brain drain within the movement itself and a breakdown of moral authority among potential sympathizers from without. That means that the movement cannot hope to grow in the future, leading to a narrow focus on maintaining past gains with no real imaginative horizon. The politics of the purge is a politics of the state of emergency, which is ultimately a politics of self-destruction.
The existence of this dynamic is not necessarily an argument against radical politics. It does highlight the challenges that such movements face. Any solution to this problem cannot take place sheerly on the level of moral exhortation of individuals or groups — systemic problems have systemic solutions. What those solutions are, however, I don’t claim to know.
An und für sich 
We need people to propose radical solutions. Most of those people are not radical in the sense that they believe their solution is to be carried out exactly as they propose. Isn’t the structural problem that the radical ideas need radical people (hence radical politics) to get to the agenda? At the time you get the two radicals together there really is no interest anymore in becoming majoritarian at any point in time. It’s about “the” truth, no further debate (hence no politics in the strict sense) helpful.
Many radical solutions get promoted by many people without getting at all close to becoming personally radicalized. As long as there’s enough of a movement to ensure steps are taken in the right direction. It’s hard for these people though to navigate between the possible circular firing squads and their own frustration with lack of progress radicalizing them (potentially into organizing a circular firing squad).
The real radical politics issue though is that the establishment is more and more becoming radicalized and closed to debate. They can fund themselves a temporary majority and organize real firing squads.