Soil loss can be significant on steep slopes, but can be reduced. Impacts from trails are confined to a narrow band. Steep, shaded slopes are difficult to maintain. Volume of use is a major factor in the level of impact. High use requires intensive management.
Narrow trails mean less impact.
Because of the very high levels of use at SKM, things must be done there that probably are not appropriate elsewhere. There is less conflict in Wisconsin than there was five years ago. However, taking trails with existing user groups and designating them as mountain bike trails is a recipe for trouble.