A “body activism” movement, with roots in fat activism and body positivity, has developed in Sweden during the last decade. As new forms of activism emerge, boundaries and approaches are being negotiated. Who is the movement for? Who can engage in it, and how? Through semi-structured interviews, we seek to understand how young Swedes who follow and engage in “body activism” on social media experience and reflect on the activism, belonging and entitlement, and their own participation. The informants discussed activism in terms of inclusiveness and political potential, where the most accessible activism is also the one ascribed with the least political potential. Entitlement is linked to collective identity, where an active participation requires belonging to the marginalised group. This article highlights the significance of boundary work in movements, where too narrowly drawn boundaries can lead to decreased participation and result in an unexploited potential for social change.