Oh, oh, and let's not forget...Music listen to? Movies see? Why not to go to bars? After-school sports? Chess?
If a person is doing this, haven't they the time to be in field service? Time is short. Especially if they're playing chess! (Well, if their opponent doesn't know what they're doing, well....)
I tend to reason it this way. They are the one's who would benefit most from having active members wear the "sack cloth", as they would be sure among themselves who they could speak to and associate with. This constant worry must be driving them up the wall, not knowing if they have associated with an apostate. Oh my!
Whenever it would benefit them or suit their purpose, they could choose not to wear the sack cloth, so they could be apart of the world that they claim to hate so much, while hoping that BIG BROTHER is not watching too closely.
Yes, certainly, we already know them by their deeds. "Wolves in sheeps clothing" comes to mind here.