It is not the case here. As few as 2 riders often ride abreast, and don't fall into single file even after I toot to let them know I'm coming. (Sometimes they do.) And groups greater than 4-5 almost always spread out to take the whole lane. I'm not talking about rights. I'm talking about courtesy. But isn't there a point where my rights become suspect when they infringe upon your rights?
Regarding "spending time with your thoughts", somehow it's hard to believe that contemplation is the goal when there are more loud conversations in those herds than on a school bus. 20-50 people wearing neon spandex, shouting to each other in 10 different conversations, blocking traffic for miles and totally oblivious or unconcerned about anyone else... I don't believe the quiet contemplation you mention is an issue here.
I was actually deep in thought on this topic just this morning on my morning ride.
I don't know where you all live or what the laws are there, but in Wisconsin bicyclists have as much right to the road as any motor vehicle. In fact, additional protections are afforded them (as it should be since they are riding 15-30 pound machines while auto drivers are operating 3000-5000 pound machines). The DOT here actually instructs cyclists to "take the lane" because there is much less risk of injury. The law further requires cars passing cyclists to leave at least 3 feet distance between them and the cyclist.
I don't think it is "discourteous" for a cyclist to obey local law even if that impedes the motoring public. If they do not obey the law that is another story, but more times than not I find the majority of discourtesy coming from motorists who are mad that they had to wait for a clean space to get around a bike. I have been almost T-boned by a police SUV who decided (without lights and sirens) to run a red light, and then refused to even acknowledge me when I looked in his window at the next stop light and shrugged at him. I have been honked at and had cars pass me in two lane roads with half their vehicle over the lane line just to give me a scare (despite the left lane being wide open). Just this morning, an oncoming truck found it hilarious to turn on his brights 100 feet in front of me. He hadn't had them on for the prior 1/2 mile that I could see him.
Simply put, here state law tells me I can, and state agencies suggest that I ride in the middle of the lane. If you want to call that discourteous, fine, I call it safe cycling practice. I am not going to put myself in further danger to ease the passing of a car-- which by the way, is a pretty simple matter. Unless you live near many world class cyclists, the riders you encounter are likely traveling under 20-25 mph. It is not much of a task for a vehicle to make that pass. Although it sounds simple to suggest that cyclists hug the shoulder (and when it is possible I do move over to ease passing), that ignores the increased risk of cross traffic obstacles which are easier for a cyclist to see and react to from the center. It also ignores the fact that there is much more road debris (gravel, glass, cans, etc.) near the shoulder.
I think this all boils down to patience, of which most of us (including myself) find it increasingly more difficult to maintain. I ride very early in the morning as a result of my work schedule. That gives me the added benefit of avoiding as many motorists as possible. I will admit that I don't obey all traffic lights at that time of day. When I ride during the day, I absolutely do. I feel that in the morning, there is no reason to sit and wait at a light when there is nobody around. I also understand that a lot of cyclists do not obey the rules of the road regardless of the time of day. That frustrates me when I am driving and as a cyclist and understand it can have an effect on patience. Still, in most circumstances I think motorists just need to understand that they have the upper hand and should exercise more restraint.
That said, if a peloton of club riders are taking up the entire road and riding with their fingers up, call the cops. They give cyclists a bad name. Just do me a favor, and pay attention to and similarly report the jerks that infringe on cyclists' safety as well.