The faster scouts will want to hike to the next trail intersection and wait for the slower hikers. The way to prevent the crew from separating is to not allow it to happen during shakedowns. Tell the crew that if someone stepped on a rattlesnake, they would have to wait for the first aid kit anyway.
Parents can relate to that.
Allowing faster hikers to hike ahead of the crew does not promote crew camaraderie. When it rains at Philmont, the temperature dips into the 50's and the wind picks up, all the ingredients for hypothermia. If the crew is on the trail during this period, the crew must continue to hike without breaks in order to maintain body heat. While the crew will hike at the slowest hiker's pace, it is each hiker's responsibility to be in shape. The out of shape hiker must be resolved to intensify his exercise program or not participate with the crew.