I can't really defend the actions of the group and really don't like any form of paceline on a bike path. My problem with SART is that much of the funding is as a bicycle commuter trail, and that's what it should be. Multi use doesn't reallly work because bicycles do not stop on a dime or turn quickly, and many walkers (especially dogs and 5 years olds) make poor decisions on the trail. Politicians don't want to hear that because its not the solution that makes everyone happy however separating bikes, cars, and pedestrians is the safest solution.
Luckily the SART out here in San Bernardino is relatively empty, being the fattest county in the state means no walkers!