Under the European Convention on Human Rights, individuals who adopt an extremist position have the same right as anyone else to freedom of thought, conscience and religion, freedom of expression and protection against discrimination, however peculiar or strange their position may seem to others. However, when an individual adopts an extremist position that undermines, threatens or violates the human rights and freedoms of others, involves undemocratic methods or aims to introduce undemocratic social or political change, restrictions must be imposed. Such restrictions must be prescribed by law, necessary to protect others in a democratic society, and proportionate to that necessity.”.
Source: Council of Europe, https://rm.coe.int/document-d-orientation-6-les-ccd-et-le-renforcement-de-la-resilience-f/16809940fc