Saturation of moral language predicts lower content engagement on social media.

Moral language often travels widely online, but does more moral content always correspond to higher engagement? We analysed 1,621,147 observations across 13 socio-political topics on Twitter (n = 530,104), Reddit (n = 1,048,653) and 8chan (n = 42,390). Using Distributed Dictionary Representations-word embeddings scored against an expert-validated moral dictionary-we measured moral loading (that is, a post's overall moral relevance) and moral density (that is, concentration of moral content across words). Negative-binomial models showed that moral loading was positively associated with engagement (range 1.12 [0.96, 1.28] to 9.07 [8.21, 9.93], all P < 0.001). Conditional on moral loading, however, moral density was 'negatively' associated with engagement (range -4.71 [-5.41, -4.02] to -0.40 [-0.52, -0.27], all P < 0.001). Engagement peaked at density 0.30 [0.30048, 0.30070], P < 0.001, with lower engagement below (2.28-fold) and above (2.78-fold), consistent with an engagement advantage for moral language that is bounded by an overmoralization penalty pattern.