Critical Mass is a largely docile group of cycling enthusiasts that ride together in mass quantities to bring awareness to issues that they feel are important to them with regard to the safety of riders or other things impacting the cycling community. As a result of their large numbers, there have been controversies that have sprung up in the past, which have often blurred the lines for people as to whether or not they should support the riders.
The biggest problem surrounding Critical Mass is the fact that they have the potential to block traffic. This can cause frustration for motorists, which can in turn lead to verbal or physical altercation. While this is something that is incredibly rare in the world of Critical Mass cycling, it is something that has the potential to exist, and therefore is an important part of the history of Critical Mass, for better or for worse.
Examples of conflicts between Critical Mass cyclists and non-cyclists have taken place all over the world, with high-profile examples coming from Europe and North America especially. One such example was the Critical Massacre in Buffalo, New York back in 2003, where cyclists were arrested after voicing their displeasure with a police officer who ticketed two riders for failing to yield to an emergency vehicle.
Other examples of discord between cyclists and motorists occurred in places like Berkeley, California, where an elderly man tried to drive through a group of cyclists as he was sick of waiting for the Critical Mass riders to finish crossing the street at an intersection. This led to a rather gruesome display, as the riders then attacked the car of the man, breaking windows, pounding on the hood and even allegedly throwing their bikes under the vehicle. While the man was wrong to have done what he did, retaliating in such a way is never the right answer either.
The main criticism against Critical Mass riders is the fact that they can block the road when such a large quantity of them are riding in one place or crossing a street. However, many Critical Mass riders would argue that they are simply doing to motorists what motorists do to them all the time by taking up a disproportionately large section of the road. Right or wrong, as long as things remain nonviolent, there is a middle ground to be had between motorists and cyclists more often than not.