Piety, is it a desirable quality?

Piety, is defined as a "belief, accepted with unthinking conventional reverence." It usually is considered essential to organised religion.

The keywords here are "unthinking" & "belief." Usually people are pious to acquire health, wealth, progeny & other purely worldly benefits from the Almighty. It is overlooked that the ultimate goal of Hinduism is "Moksha", or liberation from the cycle of birth & death. Similarly union with Christ is the true goal of a Christian as elucidated by Thomas a Kempis & William Law. Even the Quran says (64:15), "Your wealth & children are but a temptation. In your spouses & in your children, you have an enemy. Only Allah is compassionate."

In Hindu mythology, most demons were very pious. Ravana, a Brahmin, did many austerities to make him almost invincible. Hiranyakashipu, father of Prahlada also likewise. Lord Shiva was reputed to confer any boons on pious people undergoing requisite austerities, which they later used for undesirable ends. During the Spanish Inquisition, pious Christian Church functionaries committed unspeakable atrocities in others. The Quran also exhorts pious believers to abjure non-believers.

To sum up being pious may bring at best worldly benefits and at worst develop intolerance & actual harm to those of a different faith. It has nothing to do with spirituality, which confers universal benevolence & raises the human to the divine.