Someone in chutz l’aretz has a large piece of open land that he wants to sell. However the buyer is a goy that wants to build there a sort of “school” for training christian leaders. Is there anything wrong with this? What about if it was for a religion that was mamash avodah zara?
There is no problem with selling land outside Israel to non-Jews, even to idol-worshipers. There is a prohibition on selling land in Israel to idol-worshipers, and this clearly implies that this will not be an issue outside Israel.
If there will be an issue of actual idolatry – the place is designated for idol-worshiping – there is room to consider the prohibition of lifnei iver, which applies even to non-Jews. However, if other plots of land are available, the prohibition of lifnei iver will not apply.
Although there is a special prohibition of selling items for the purpose of idolatry, this applies to items that are designated as idols or are part of the idolatry ceremony, and not to selling a “neutral” piece of land. See Rambam, Avodah Zarah Chap. 8 and Shulchan Aruch, Yoreh De’ah 151.
Likewise, there is a prohibition against selling a shul to idolatry (see Iggros Moshe Orach Chaim 2:45), and this shows that the prohibition does not apply to regular plots of land.