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.
Left-wing politics
In several countries, the terms far-left and radical left have been associated with varieties of communism, autonomism and anarchism. They have been used to describe groups that advocate anti-capitalism or eco-terrorism. In France, a distinction is made between the left (Socialist Party and Communist Party) and the far-left (Trotskyists, Maoists and anarchists). The United States Department of Homeland Security defines left-wing extremism as groups that want "to bring about change through violent revolution rather than through established political processes".