Web Content Accessibility Guidelines (WCAG) require digital diagrams to be tagged with screen readable text descriptions for access by blind and partially sighted individuals (BPSI). The aim of these guidelines is to comply with human rights-based accessibility legislation, which aims to preserve the normative agency of BPSI (the ability to reflect on, evaluate and act upon a conception of what constitutes a worthwhile life for themselves). However, theories from the Diagrams community suggest that text and diagrams offer distinctly different constraints. For example, Shimojima’s Constraint Hypothesis (the relationship of structural constraints to target problem constraints in a mode of representation establish the variance of inferential potential) and the interrelated free ride phenomenon (additional inferences can be made in a representation if the relationship of constraints is a good match). Therefore, a guideline that requires the text description of a diagram (such as via the WCAG) might limit the normative agency diagram users who are BPSI. Despite the apparent necessity of providing non-visual alternatives of diagrammatic properties for accessibility, they are rarely explored or developed sufficiently to be consistently provided to BPSI. Thus, we argue that the affordances of diagrammatic representations provide possibilities for normative agency that are lost if not represented non-visually in diagrams designed for accessibility.