As the title suggests, psychopaths are qualitatively different from other people, literally having no conscience.
This website which seems to be an information resource for psychopathy states:
Imagine - if you can - not having a conscience, none at all, no feelings of guilt or remorse no matter what you do, no limiting sense of concern for the well-being of strangers, friends, or even family members. Imagine no struggles with shame, not a single one in your whole life, no matter what kind of selfish, lazy, harmful, or immoral action you had taken.
I think it is well established that psychopaths lack empathy, which has been shown with differences in brain structure and/or activity, although I don't think it is necessarily valid to conclude that psychopaths have no conscience from that.
The definition for conscience is not dependent on empathy, bur rather knowing or having a sense of what is right or wrong. Even with a complete lack of empathy or remorse, why could there be no sense of right and wrong?
Is there any validity to the claim that psychopaths lack a conscience? Why would they be unable to have the same values of wrong and right instilled as other people, or to sense how people will morally view their actions?