Remember kids, Tankies wants to undermine democracy - same as facists.
factionalism
You sure you aren't a tankie or why else would you use the word with a negative connotation? When two actual leftists meet there's going to be three factions, yes, but shit is still going to get done. Factions means plurality, plurality means diversity of tactics, all that is good shit.
And I guarantee you there are MLs participating in black bloc protests
MLs, yes. As in Trots and stuff. But actual tankies? Nope. That would require a capacity to cooperate, they even discourage participation internally (mostly by claiming it's a waste of time, doesn't contribute to the revolution, whatnot) as it's dangerous to them, in the sense that people who have not yet completely bought into the cult might choose praxis over brainwashing: Those things are by and large run by Anarchists, with Anarchist organisation principles, and that shit working flies right into the face of democratic centralism.