The term sacred cow is an idiom, a figurative reference to sacred cows in some religions. This idiom is thought to originate in American English, although similar or even identical idioms occur in many other languages.
The idiom is based on the popular understanding of the elevated place of cows in Hinduism. A literal sacred cow or sacred bull is an actual cow or bull that is treated with sincere reverence. A figurative sacred cow is something else that is considered unreasonably immune from question or criticism.
There in no topic, doctrine or person that is above question or criticism. Any topic, doctrine, or person is subject to question and criticism, regardless if it is considered orthodox or not. This is indeed scriptural. The Scriptures are our highest authority and our guide to examine and test everything else in this world.
Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world.
(1 John 4:1 ESV)
Every word of God proves true; he is a shield to those who take refuge in him. Do not add to his words, lest he rebuke you and you be found a liar.
(Proverbs 30:5-6 ESV)
No sacred cows should be considered safe, it’s open season and there are no bag limits. After all, sacred cows make the best hamburger.