About 130 people were injured during a violent clash during protests against the importation of American Beef into South Korea. By now, most of the moderates who participated in the protests are probably tired of them and need to go back to their own lives, so it's not a particular surprise that only the hardcore protestors would still go on. So it would have only been a matter of time before the ongoing protests resulted in violence.
The ironic thing is that for all we know, the injuries from this single protest might be more harm than what could result from the import of US beef, at least in terms of Creutzfeldt-Jakob disease infection. It is quite possible that no such cases might arise at all. I could be wrong, and the protestors could be right in their belief that import of US beef could result in a rash of cases, but there is no indication that this would be the case.