SINGAPORE, March 3 -- A call for kindness at the entrance of the Kampong Glam Ramadan Bazaar in Singapore has ignited a lively argument over how far food reviewers should go, after a banner urging social-media users to avoid posting negative comments went viral.

The sign, which went viral on social media, tells visitors who enjoyed their meals to share praise publicly, but asks unhappy customers to raise complaints privately.

"We strive for perfection, but we are only human," the banner reads.

"If you feel inclined to leave a negative review, we humbly ask for the opportunity to make it right first. Be human first, influence later."

The message, accompanied by a reference to Islamic teachings on compassion, was put up by Sheikh Ali Re...