Very few in America today would smile upon someone donning blackface and performing minstrelsy's greatest hits.  It would be an unfair attack on an oppressed minority, and African Americans would be (rightly) be furious.  Nevertheless, the performer, no matter how wrong, would probably not get death threats and would be eventually (after the shock value wore off) ignored.  That is the difference.  Picketing, protesting, boycotts...all fine.  Opposing hate speech with rioting, embassy-burnings (in Syria's case almost certainly government-condoned), and threats against innocent people who just happen to share the perpetrator's nationality...those are wrong no matter the extentuating background circumstances.