That is, when it happens to show that someone is a mental retard and as such shouldn’t be executed for murder.
Just the old liberal hamster wheel logic in action.
I’m actually quite indifferent to the DP. But I’m not indifferent to using mental retardation as a defense. If anything it is more of a reason to execute the murderer as the very dull operate by instinct and emotion, not cost/benefit calculations, and as such cannot be expected to reform and make positive contributions to society even if provided with incentives to do so.
The other reason is shown by the graph above. Stupid people are simply far, far more likely to be criminals than normal people. Making retardation a defense against the DP effectively puts the most criminally prone cognitive fraction of the American population above the law.