Word, I went to a game while I was there, and nothing happened really, except some MP's took away some trouble makers and what not. But still, as you said they aren't fuckin around. I was sitting in the section for Sao Paulo fans (which is not the team I route for, I route for Corinthians but of course didn't say shit cuz I like to breathe)...but yeah, it was such an intense vibe and I just would not want to get caught in the middle of some big fight there.
There were some fans mock fighting, one guy taking another's cap and shirt and playing monkey in the middle, a lot of pushing and shoving, som punching and kicking, then the next second smiling and hand shaking, then back to the mock fighting...people were looking over, and this is a few rows down from me (place was paaacked)...I thought something would go down for sure.
Still, Brazil is great, I love it there and want to go back, just gotta be safe and smart. If you go symbols, consider the north east of the country, places like Fortaleza, Bahia, Salvador, Recife. It's nice there year round and the beaches are all with that clear blue water, real afro-centric areas (esp Bahia).