Taking the lane is one thing, but taking the whole lane for no reason other than you can if there is enough of you in the group, as I see it is just plain wrong.
After complaints from motorists, police in Winter Park, Florida were out with video cameras. What they filmed made to the news on an Orlando station.
At the start of the piece, I saw cyclists three or four abreast; at least one rider completely over the double yellow line. About twenty cars backed up behind the riders.
Then I saw the entire pack blow through a stop sign, and make a right, at a very high rate of speed even though there was other traffic passing.
It looked to me that this was an unofficial race, rather than a group-training ride. Here is the link, view for yourself and be your own judge.
Actually, in a large group like this it is often safer to ride two abreast. They can do so taking up half the lane, which gives motorists a chance to see around the group to determine if it is safe to pass.
Riding single file a group is twice as long, and takes twice as long to pass.
Stronger riders can stay at the front if they wish and change off by having one line constantly moving forward, and the other dropping back. Wind direction usually decides which line moves forward. (Picture left.)
Going through stop signs and lights, the whole group stops, and then moves off as a group, as if they were one vehicle.