There’s a difference between working for a nonbeliever and giving aid and comfort to a cultist whose mission it is to cause people to believe in a false god and a false christ. I would not voluntarily choose to work under such a person. Paul says we cannot avoid contact with unbelievers. But neither can we avoid the Apostolic warning against giving even a greeting to one who brings a false Gospel. See 1 John 1:10-11. If we collaborate with these folks, we share in their guilt. Don’t get mad at me. Take it up with the Apostle John. Going soft on false Gospels is not an option. We cannot trade eternal human souls for short term political gain. It’s wrong.
John is speaking obviously of spiritual collaboration, not upon cooperation in earthly endeavors.
Surely John also wanted his readers to understand his context. This is no mere social hello. This is a churchly greeting.