Varieties of criticism
Conservative criticism has nothing much to do with "left-wing" or "right-wing", because left-wing people are often very conservative, in the defined sense, while right-wing people can also be very radical, in the defined sense. The difference between "radical" and "conservative" has more to do with the belief in whether "a change to something genuinely new" is really possible and necessary. Radicals typically believe strongly that such change is highly desirable and necessary, and that it can be achieved. Their criticism is that there is "not enough" change. Conservative critics, by contrast, are very skeptical about any such change, because they feel the change is really "just another form" of something that already exists.
Ted Kaczynski
Throughout the document, Kaczynski addresses leftism as a movement. He defines leftists as "mainly socialists, collectivists, 'politically correct' types, feminists, gay and disability activists, animal rights activists and the like," states that leftism is driven primarily by "feelings of inferiority" and "oversocialization," and derides leftism as "one of the most widespread manifestations of the craziness of our world." Kaczynski additionally states that "a movement that exalts nature and opposes technology must take a resolutely anti-leftist stance and must avoid all collaboration with leftists," as in his view "[l]eftism is in the long run inconsistent with wild nature, with human freedom and with the elimination of modern technology." He also criticizes conservatives, describing them as "fools" who "whine about the decay of traditional values, yet they enthusiastically support technological progress and economic growth. Apparently, it never occurs to them that you can't make rapid, drastic changes in the technology and the economy of a society without causing rapid changes in all other aspects of the society as well, and that such rapid changes inevitably break down traditional values."