It's not always the case that providing protection to a group of villagers means a demon is good; sometimes they're just keeping them as reserve rations.
Karma is the most direct standard to determine if a creature is evil.
Anyone plagued by karma is generally notorious for their crimes, with very few exceptions. The most representative figure among them is the Ming River Sect Master who became Supreme.
The Blood Sea is the filthiest place in the world, yet within it lies a top-grade Innate Spiritual Treasure, the Karma Fire Red Lotus.
This treasure automatically absorbs the karma of the world, using it as nourishment to enhance its power. Naturally, the Ming River Sect Master, who obtained it, was covered in karma.
However, the Karma Fire Red Lotus can suppress fortune, so the Ming River Sect Master was never burdened by karma. This is why he dared to plot against Red Cloud back in the day, attempting to seize the Foundation of Sanctum Hongmeng Purple Qi from him.
