1. Anarchists really don't seem to be escalating anything in Ferguson. Everything I've heard from anarchists around the area (St. Louis specifically) sounds like they view it as something to participate in as people who hate the police, but not as something to 'make an intervention in.'
2. The reason you think this isn't the case is that the forces of order have found that the concept of the 'outside agitator' is the most useful ideological tool to crush rebellion. Divide and Conquer: it's a cliche for a reason. For example, Martin Luther King was called an outside agitator during the Civil Rights movement (read his "Letter From Birmingham Jail.')
3. Outside Agitator works well not only because the obvious forces of power (the state, media, capitalists) want to crush the rebellion, but critically it strengthens local 'community leadership.' In the US this often takes the form of churches, non-profits, and occasionally unions. These groups inhabit have some sort of power and what they say carries some currency amongst marginalized people of revolt. By calling 'outside agitators' they are both rewarded by the former obvious power centers and they solidify themselves as the singular heroes of the situation.
4. Social Justice Warriors on tumblr, twitter, and occasionally real life have adopted this rhetoric, mostly because they're liberals who have, for the first time in decades, been given a rhetoric that sounds remotely sincere (privilege, oppression, etc), and they are going to milk it for all its worth.
5. This is possibly just hearsay, but supposedly many people in Ferugson don't buy the outside agitator stuff. If anything, they're more mad at people like jesse jackson and al sharpton who are usually the leaders of deploying that rhetoric. https://www.youtube.com/watch?v=dYqTCz1-W1s