They reject incrementalism as conceding to the chuds, the only path is always an immediate revolution to the most extreme form of delusional utopia.
As an anarchist libertarian I'm quite familiar with this idea (except that the utopia is proven scientific fact) as many otherwise smart anarchists completely lose their shit at the idea of ever conceding to statists even as the ratchet of the state has only progressed in one direction while they've demanded purity and the "traitors" they scoff at (Hayek and Friedman most notably) were the only ones to ever receive mainstream attention and acceptance and get any ideas against that ratchet into the larger discourse. I admit I'm naturally inclined to incrementalism and evolution over revolution but I've never quite understood the argument that forcing the "contradictions" to the forefront (especially violently) will lead to the result you want, it's not historically supported at all (seriously try to find the examples) and, in the specific anarchist case, nor can I square the arguments against central planning as not applying to a centrally planned revolution for establishing a new system which seems like a pretty fatal conceit to me.