If it is like the WTO/G8 meetings they riot at, there are a number of foreigners who come here to riot. They should be denied travel visas into America. There are BANDS that still cannot tour the US because of 30 year old pot charges. There is no reason to let violent anarchists come in here.
There's just something about the way they carry themselves, and the violence of their reactions that strike me as "eurotrash".
I have no doubt that there are "Putin-bucks" invested in their training and travel, they probably have more passports and ID's than you can imagine.