From the article: "At this moment, if the rider who is passing the dog flashes his brake lights and/or puts an arm up to alert the following riders, this becomes the world’s most boring GoPro video. But he doesn’t. Come on, guys. You're riding with friends. Help them out."
I mentioned that (someone up front, pointing out the dog to those behind) when someone posted this on facebook and was flamed for suggesting that someone could have warned the riders behind him. To the flamers, that was impossible to do.
We ride with large groups, regularly. The lead, at least one road captain in the middle, and the sweep are always in radio contact, and several others also have radios - but stay off them, if not designated road captains for the day's ride. There is no "chatter" on the radios - they are used for safety and to maintain group integrity. Anytime someone sees an animal or other hazard on the side of the road, they either signal, or, if they have a radio, signal and say what it is, and it gets passed down the line. Is it a guarantee of safety? No, but it is great when it does work. There is always a pre-ride safety brief, and the opportunity for questions.
Group riding is no more dangerous than riding alone, and if you are familiar with the others in the group, and know their riding styles, is somewhat safer. I like riding alone - and I like riding with my friends. Yesterday, we rode with 20 Spyders and a 2 wheel BMW - and we all survived the group ride.