GERLACH, Nev.—One of the main principles of Burning Man is “radical inclusion,” but organizers of the annual festival in the desert are taking radical exception to new government proposals they say would kill its countercultural spirit.

Concerned that it is vulnerable to a mass-casualty attack, the Bureau of Land Management wants to encircle Burning Man’s makeshift desert town with thousands of physical barriers and have security guards screen attendees, called “Burners,” for contraband. The agency, which manages the federal...