We just had a death on the road, from a driver hitting a cyclist in a group. I'm a life-long cyclists, and I now am somewhat fearful about cycling on the road. I see so many groups that take an entire lane and not even care about the cars behind them - it's easy to understand the frustration of the drivers. It's a knotty problem, I wish we had more bicycle lanes.
Obviously I wasn't there for the "taking the lane" circumstances you've seen, but where I live there are very few sections of road where it would be safe for a vehicle to attempt to occupy the lane while a group of cyclists are in it, and cars should be overtaking instead. It's no more difficult for a car to overtake when the cyclists are "taking the lane."