Oh and I actually think anyone riding in fast group should be known by at least one of the others.
Last 2 rides we have had some non-OR riders in our group. In one ride one went down (he had no business riding with us), this rider was riding over his head.
The 2nd time we had riders who disrespected others by riding like an asshat. Same group, we had a rider that: knew his limit, chose to ride in the back of the pack, was level headed, and respectful (UP brought him). I am willing to let them ride with us if they can respect the ride and group.
This is why I sweep, I don't want people up my ass and I carry the 1st aid kit.