For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
The full scripture reads:
1 Corinthians 12:4-11
SPIRITUAL GIFTS
4 e There are diversities of gifts, but the same Spirit. 5 There are differences of ministries, but the same Lord. 6 And there are diversities of activities, but it is the same God who works all in all. 7 But the manifestation of the Spirit is given to each one for the profit of all: 8 for to one is given the word of wisdom through the Spirit, to another the word of knowledge through the same Spirit, 9 to another faith by the same Spirit, to another gifts of healings by the same Spirit, 10 to another the working of miracles, to another prophecy, to another discerning of spirits, to another different kinds of tongues, to another the interpretation of tongues. 11 But one and the same Spirit works all these things, distributing to each one individually as He wills.
In other words not every person has a 'discerning of spirits' or any of the other gifts. They all come from the same place but not distributed equally 100% among all. That is what makes all of us different and unique as He wills it. And we may use the gifts of the Spirit for good works, but some people do not know how to or choose not to.