A Stand Alone Complex can be compared to the emergent copycat behavior that often occurs after incidents such as serial murders or terrorist attacks. An incident catches the public's attention and certain types of people "get on the bandwagon", so to speak. It is particularly apparent when the incident appears to be the result of well-known political or religious beliefs, but it can also occur in response to intense media attention. For example, a mere fire, no matter the number of deaths, is just a garden variety tragedy. However, if the right kind of people begin to believe it was arson, caused by deliberate action, the threat that more arsons will be committed increases dramatically.
What separates the Stand Alone Complex from normal copycat behavior is that there is no real originator of the copied action, but merely a rumor or an illusion that supposedly performed the copied action. There may be real people who are labeled as the originator, but in reality, no one started the original behavior. And in Stand Alone Complex, the facade just has to exist in the minds of the public. In other words, a potential copycat just has to believe the copied behavior happened from an originator - when it really did not. The result is an epidemic of copied behavior having a net effect of purpose. One could say that the Stand Alone Complex is mass hysteria over nothing - yet causing an overall change in social structure.
This is not unlike the concepts of memes (refer to the conversation between the major and the Puppet Master in the manga) and second-order simulacra. It also has ties to social theory, as illustrated in the work of Frederic Jameson and Masachi Osawa. The Slender Man phenomenon, in which the fictitious concept of a supernatural murderer went viral and has allegedly inspired real attacks, may be seen as an example of the Stand Alone Complex.
It is only a matter of time before this becomes reality. And nothing can stop it.
My real name, who I really am is Cigma and I hope I am wrong
Neat. Sounds subversive.