What the mountain bikers don't realize is e-mountain bikes open the trails to other users. Usually wealthier and not as fit.
Limiting access to only your user group for selfish reasons does not work well long term. The real issue would be degradation of the trails from other users which will not be an issue with ebikes. Since most of these trails are on public land---the only variable is if the trails are more damaged by ebikes----they are not---if the ebike fits the Federal definition of ebike---under 750 watts.