States have negative and positive obligations regarding peaceful demonstrations. The negative obligation is that the state and the police can not interfere and ban any peaceful demonstration. The positive obligation is to help and protect peaceful demonstrations, by coordinating traffic, keeping public order and protecting protesters from those wishing to disturb the demonstration.
There are demonstrations that happen that go unnoticed by the police, either because they come about spontaneously or because the demonstration was banned. It should be emphasised, however, that a lack of notice in and of itself does not give the state a free pass to use force against peaceful demonstrators. If a demonstration is considered to be unlawful – because of a lack of notice – that does not mean that the police are automatically entitled to intervene. If a demonstration is peaceful, there is no justification to interfere.
A benefit to society
States may not limit freedom of assembly just because the organisers want to express ideas that are not popular, or because those in power think that the ideas at hand would go against the interests of society in the long run. Of course, when public safety is endangered, states may legitimately break up a demonstration. When, for example, a demonstration that started peacefully becomes violent, such as when people set cars on fire or break into shops, the police may legitimately use force to break up the crowd, thereby protecting the property and physical well being of other citizens. But the force the state employs in such cases should never exceed the minimal force needed to restore normalcy.
Society benefits from letting free assemblies take place in crucial ways. Freedom of assembly is an important means through which the public can express their views to their leaders and to other members of society. It promotes public discourse and diversity, and it is also a proper tool to achieve changes in society.
Because holding a march requires relatively fewer resources compared to other ways of efficiently communicating a message, it is frequently used by the powerless who cannot otherwise make their voice heard. Demonstrations may inconvenience us, such as when we are trying to get to work and the fastest route to our workplace is closed down due to the event. This can be truly annoying. But because we are living together in a society, we should remember how important it is that all of us have a say in what we do and how we do it. When people are denied this right to speak up, they are denied their dignity.