The body-positive movement is one of many decentralized, user-generated movements on social media that seek to engender positive societal change. In support of the body-positive movement, social media users employ a variety of messages and images to advocate for more inclusive beauty standards across different online platforms. We examine how the nature of body-positive messaging (mainstream body positivity vs body neutrality), the degree to which images are sexualized (sexualized vs non-sexualized), and the platform that hosts body-positive content (Instagram/Flickr/blog) influence how people evaluate body-positive content online. The results indicate that the more participants felt messaging was body-neutral, the more morally appropriate and less self-interested they found the posts. The extent to which participants felt messaging was morally appropriate also led them to embrace more inclusive beauty standards. Moreover, non-sexualized (vs sexualized) images were rated more morally appropriate and less self-interested. Implications for promoting body positivity and other prosocial movements online are discussed.