Just to bring some balance, here is Jesus' words about a similar issue:
Mark 9
38 John said to him: “Teacher, we saw someone expelling demons by using your name, and we tried to prevent him, because he was not following us.”
+ 39 But Jesus said: “Do not try to prevent him, for there is no one who will do a powerful work on the basis of my name who will quickly be able to say anything bad about me.
40 For whoever is not against us is for us.
+ 41 And whoever gives you a cup of water to drink because you belong to Christ,
+ I tell you truly, he will by no means lose his reward.
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