With that said, here is a list of just a few of the many historical protests that by today's standards may or may not be considered "rioting" just to remind everyone that it isn't new, it isn't different, and sometimes, yes, it is effective.
The Boston Tea PartyThe Boston Tea Party was a "riot." It was theft and vandalism and it was relatively violent. Protesters dumped an entire shipment of tea into the Boston Harbor to protest taxes (which was a big deal, but not anything like police brutality or murder). The British government's response to this riot led to the American Revolution (an extremely violent series of events that cost many lives but ultimately resulted in the United States).
The Protestant ReformationThe Protestant Reformation started out as a peaceful protest (pamphlet distribution is hard core) but led to a series of religious wars, culminating in the Thirty Years War, one of the most destructive (and longest) conflicts in European history.
The Storming of the BastilleThe Bastille was a medieval fortress and prison in Paris that was a symbol of royal authority. Protestors stormed the Bastille as a protest against abuses of the monarchy, overtook the prison, lynched several defenders and beheaded the Governor. This sparked the French Revolution and is celebrated every July 14 in France as a national holiday.
Bloody SundayIn 1905, a peaceful march of Russian citizens protesting the oppressive Russian monarchy turned into a violent confrontation with Russian troops. This event inspired even more workers to join in a labor strike which ultimately led to a Russian revolution.
The Stonewall RiotsThe Stonewall riots were sparked by a June 1969 police raid of the Stonewall Inn in Greenwich Village. The patrons of the bar refused to cooperate and the police quickly lost control of the situation. The protests turned violent but are considered a major catalyst of the LGBT rights movement in the U.S. Today Gay Pride events are held annually in June to commemorate the Stonewall riots.
The Haymarket RiotThe day before the demonstration at Haymarket Square, several striking workers had been killed by police. What started as a peaceful labor demonstration turned violent. Although several anarchists were sentenced to death as a result, the incident had a massive effect on the labor movement.
The Watts RiotIn 1965 a young black man was pulled over by police and arrested, while a crowd of onlookers gathered. Tensions were high and it turned to violence, setting off a large-scale series of riots that lasted several days and were extremely costly. An official investigation, prompted by the Governor, found that the Watts riots were the result of the community's longstanding grievances over social and economic conditions. Many consider these riots to be a key turning point in the African-American Civil Rights Movement.
Uprising in TunisiaProtests in Tunisia about government corruption, high inflation and unemployment rates surged when one man set himself on fire after police confiscated his vegetable cart (his only means of living). The situation escalated as protests continued to grow and over 300 people died. The president (who had ruled for 23 years) fled the country and Tunisia held its first free election. Similar protests and governmental reforms took place throughout North Africa and many consider this incident the catalyst that sparked the "Arab Spring."
The Women's Suffrage MovementOne of the most memorable protests of the women's suffrage movement was a rally that turned violent thanks to onlookers who attacked the suffragists. Although the protestors were the victims, not the perpetrators, the fact that so many were assaulted brought newfound attention to their cause. Attention that a peaceful parade might not have garnered.
Maybe you still think rioting is always wrong and that's fair, but hopefully you can at least understand why people have done it over the years and continue to do it. It's not like everyone has made the conscious decision "let's riot, that will help" so much as frustration and helplessness leads to attempts at getting attention by whatever means possible. Maybe it won't do any good... maybe it really is counterproductive... but at least they have their reasons and they are a hell of a lot more legitimate than some of the moronic reasons that white people have rioted lately (for example SPORTS!!).