Adding external motivation undermines those already internally motivated against prejudice.

Evidence

Specifically, people high in internal but low on external motivation to respond without prejudice are generally effective in responding without prejudice, whereas people high on both motives are much more prone to responding with prejudice (Devine et al., 2002). Key questions remain, however, concerning how or why the presence of external motivation interferes with effective control of prejudice (or why its absence leads to effective control). — , Rudman, Laurie A - On the Nature of…, 2124

Categorization

• QUESTION: Why would adding an external motive degrade an internally-driven regulator? The mechanism is unexplained — worth chasing into Devine et al. 2002.
• XREF: Echoes the crowding-out literature where extrinsic incentives suppress intrinsic motivation (Self-Determination Theory, Deci & Ryan).