How do you handle crazy people who join your action?

http://cityroom.blogs.nytimes.com/2011/12/02/a-protesters-uneasy-presence-at-occupy-wall-street/

"Mr. Watts has been arrested six times since he came to New York for Occupy Wall Street, according to his lawyer, Martin Stolar, including his arrest on Nov. 17, when he was charged with felony assault and grand larceny after the police said he threw a AAA battery at the police and stole a deputy’s hat. In October, he was charged with resisting arrest after the police said he bragged to them that he had stolen some of the orange netting they use to contain crowds. He has four separate misdemeanor charges, Mr. Stolar said."

Brandon Watts lived in group homes and with different relatives before moving to Occupy Wall Street, according to the article. The people who knew him at OWS said he wanted confrontations with the police.

So what to do if a disturbed person joins your ranks?  It can be a difficult thing, which I have little experience dealing with.  On the one hand, you don't want a crazy person doing crazy things to spoil your action. On the other hand, how does a leaderless group decide who among them are not worthy to be in the group?  I offer no easy solution.  The decision has to be done by the group, and it's not easy.