Well they are protesting a number of different things. I read some things in the New York times that sites some of the subjects of protest ranging from the displacement of marginalized populations, mistreatment of natives, the fact that IOC is a high profile
capitalist symbol of an overtly suppressive system, and some people are just jumping on the band wagon. Homeless, natives, hippie douche bags, and other interest groups are represented in the protests, but they are very poorly organized and for whatever reason
some people have resorted to violence, which is not a good thing. Protest is not always bad, but violence is.