A common reaction to political violence such as the recent student riots is that it's not necessary in a democracy, where change can be effected by the ballot box.
However, people voted for a party which gave a cast-iron guarantee not to do something which, when elected, proceeded to do.
This makes a mockery of the ballot box and leaves politically motivated people with little option but to demonstrate.
Experience has shown that peaceful demonstrations are largely ignored by the media and are entirely ignored by those in power (for example the 2m-strong Iraq war demonstration in 2003).
Nothing but rioting will make the political class pay attention and put a stop to these unnecessary cuts.