How did Richard Brandt use idealized conditions to identify rational moral desires?

In his work A Theory of the Good and the Right (1979), the philosopher Richard B. Brandt proposed that moral terms refer to the desires or preferences an individual would hold under specific idealized conditions.12

To identify these "rational moral desires," Brandt established a framework requiring that an individual be calm, reflective, possess complete knowledge of all relevant facts, and vividly appreciate the consequences of their actions for themselves and others. Crucially, Brandt included a requirement that the person be motivated only by "rational desires"—defined as those desires that would remain after the individual undergoes cognitive psychotherapy. This process is intended to enable people to better understand their existing desires and to discard those they do not wish to keep.12

Brandt used this model to ask what rules a rational person would desire to be included in an ideal moral code that all rational people could support. While this approach seeks to ground morality in rational deliberation, it has been debated whether such a standard leads to an objectivist view, as different individuals might still desire different rules even under these idealized conditions.12