Which attributes of a person contribute to their tendency to moralize others' thoughts? Adopting an individual-difference approach to moral cognition, eight studies (N = 2,033) investigated how people's ability for self-control shapes their moral reactions to others' mental states. Specifically, Studies 1a-2b found positive predictive effects of trait self-control (TSC) on the moralization (e.g., blaming) of another person's fantasies about different immoral behaviors. While ruling out alternative explanations, they furthermore supported the mediating role of ascribing targets control over their mental states. Studies 3a-3b provided correlational evidence of the perceived ability to control one's own mental states as a mechanism in the relationship between TSC and ascriptions of control to others. Studies 4a-4b followed a causal-chain experimental approach: A manipulation of participants' self-perceived ability to control their emotions impacted their control ascriptions to others over their immoral mental states (Study 4a), and targets perceived as high (vs. low) in control over their immoral mental states elicited stronger moralizing reactions. Taken together, the present studies elucidate why people moralize others' purely mental states, even in the absence of overt behavior. More broadly, they advance our knowledge about the role of individual differences, particularly in self-control, in moral cognition.