The topic statement is lifted from Glanville Williams Criminal Law: The General Part [2nd ed. 1961]. A perusal of the topic shows that it runs counter to another statement in the same text which shows the belief of the author that the concept of mens rea is an index of maturity of our legal system. The correlation to the various justifications of punishment or purposes of criminalization does not at all compute when considered from the various vantage points and time frames of the said justification theories. The mental element of crime may be significant for one purpose or the other but the same way that the various purposes do not conjoin with any one crime, the element of mens rea will not be relevant to all the justifications and purposes.
The cardinal principle of criminal law is that 'a wrongful act does not make a person guilty unless his mind is legally blameworthy.' There must not only be a wrongful act (actus reus), but with it must also concur intent (mens rea, Latin: the guilty mind; a guilty or wrongful purpose; a criminal intent1). Actus non facit reum nisi mens sit rea.2This is so because evil thoughts are condemnable and punishable only when they are sufficiently dangerous to society and only when translated into evil deeds. From a practical vantage point, there is really no way for any legal system to sanction evil thoughts. Blackstone confirmed this:
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