Most recent criticisms have been leveled at Callicott's works addressing the idea of wilderness, the "sanctum sanctorum" of the twentieth-century environmental movement. Some scholars acknowledge the intellectual merits of Callicott's critique of the wilderness idea, but regard it as both a betrayal of one of Aldo Leopold's most cherished causes and as giving aid and comfort to the environmental movement's enemies. Callicott counters that his quarrel is with an idea, not the places trammeled by the idea, the preservation of which places he appears to be as ardently supportive as any other environmentalist. In “Should Wilderness Areas Become Biodiversity Reserves,” he argues that the pressing conservation needs of the twenty-first century are better served by the biodiversity-reserve idea. This idea indicates by its very name what the primary goal of wildland preservation is, whereas the wilderness idea is historically associated with outdoor recreation and thus, Callicott claims, confuses the preservation issue and fosters incoherent and contradictory wildlands-use policies.