One of the more striking findings in recent work on political discussion among citizens has been that exposure to disagreement in discussion networks demobilises people, making political participation less likely. This runs counter to the expectations of theories of social capital and deliberative democracy, and also to the finding that exposure to cross-cutting views leads to greater tolerance of the opinions of others. This result is of great significance if it proves to be a general finding, holding in a variety of contexts and for a range of forms of political activism. This paper therefore provides a test, analysing a wide range of forms of political activism. The results suggest that it is premature to blame disagreement for demobilisation: in some circumstances, and for some forms of activism, exposure to countervailing views may actually motivate participation.