Legitimacy of environmental management and policies is an important topic in environmental research. Based on the notion of ‘regimes of justification’, we aim to analyse the dynamics in argumentations used to legitimize and de-legitimize Dutch nature conservation practices. Contrary to prior studies, we demonstrate how actors in two locations where environmental disputes arose showed little willingness to switch between arguments in order to reach a compromise. Instead, some actors constructed incompatibilities between arguments in order to delegitimize competing actors. Especially in the visioning phase, institutional actors emphasized technical efficiency, planning and global environmentalism, and arguments related to emotional accounts, inspiration and locality were de-legitimized. In the discussion, we argue that it is not the formal or informal inclusion of the actors in the process, but the construction of the legitimacy of their arguments that determines the inclusiveness and outcome of the process.