Therefore I want you to know that no one who is speaking by the Spirit of God says, “Jesus be cursed,”...
(1 Cor 12:3)
Mark 9:38-41
38 “Teacher,” said John, “we saw someone driving out demons in your name and we told him to stop, because he was not one of us.”
39 “Do not stop him,” Jesus said. “For no one who does a miracle in my name can in the next moment say anything bad about me, 40 for whoever is not against us is for us. 41 Truly I tell you, anyone who gives you a cup of water in my name because you belong to the Messiah will certainly not lose their reward.
39 “Do not stop him,” Jesus said. “For no one who does a miracle in my name can in the next moment say anything bad about me, 40 for whoever is not against us is for us. 41 Truly I tell you, anyone who gives you a cup of water in my name because you belong to the Messiah will certainly not lose their reward.
Note the difference:
Paul is attacking the ''Jesuophobes'', these Christians who adored the his same Christ but didn't name him 'Jesus'.
''Mark'' (author) is co-opting these rival Christians. If they are recognized as Christians (i.e., adoring the same Christ adored by Mark, at least in the eyes of the outsiders), then, even if they curse Jesus (since they don't accept the name ''Jesus'' for Christ), even so, they are preparing the way for the Gospel Jesus.
This betrayes an evident desire of co-optation by the evangelist.