I submit that it is not. How would your non-anonymous world stop a madman like Anders Breivik? He did not hide his views. He was a known user of white supremacist sites, and a known affiliate of white supremacist groups. However, no one, not even the fringe groups that he affiliated with could predict that he would carry out his horrible actions.
Breivik was not anonymous. That fact, however, did nothing to stop him from carrying out his crime.
Perhaps some of the misunderstanding is due to the broad definition of anonymity I'm using. Anonymity as I use it is the inability to link a person's actions to their identity. This type of anonymity breaks a lot of our social institutions. For example, if you don't know that a person committed a crime it's hard to arrest them.
If Anders Breivik was anonymous he would still be wandering Norway because no one would know that he was responsible for the murders. Some of the information I've read suggests that he wanted (or at least expected) to be caught. In such situations anonymity may actually discourage crime. I would guess, however, that most criminals would rather not be caught.
That anonymity is the source of crime isn't my argument, it's his.
Clearly, you can be identified as an 'enemy' and still be dangerous. A good example is during time of war, soldiers are often uniformed and standing in ranks. There is no doubt about which 'side' someone facing you is on, and yet they are no less dangerous because of it.
Anonymity doesn't remove danger, but merely identifies that danger exists.
Wouldn't it be interesting if you could flag something to notify you if you're walking by a white supremacist?