I've read this idom from an article, and it seems that the phrase "skewer a sacred cow" mean "to criticize" but I am not very sure.
Does anyone know the exact meaning and the origin of this idom?
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The figurative use of the term 'sacred cow', to refer to a project or process that is immune from tampering, is American in origin and also dates from the late 19th century.
Source: The Phrase Finder
To skewer a sacred cow, means to defy what is generally held as indisputable.