Since no one answered, I asked a very chashuv Rav IRL.
Apparently it's an explicit teshuva from Rav Moshe Feinstein. Igros Moshe Y"D 1:68
Rav Moshe was asked by an architect if he's allowed to draw up plans for a church. Rav Moshe paskened it's muttar m'ikar hadin. At worst, he says, it mseyah (assisting in the committing of a sin when others could have provided the same assistance) which is technically muttar by non-jews.
However, he writes that one should distance themselves from this except when there is great need.
"ונמצא שלדינא יש להתיר אבל עכ״פ מהראוי להתרחק מהכיעור ..."
Relevant video from the Bais Havaad project saying the same thing: here.