Iggrot Moshe Orach Chaim 5:13

"With regards to a business partner that does not observe the Torah that manners dictate that you should give him food and water. . . Seemingly, there is a prohibition of “[putting a stumbling block] in front of a blind person” because he will eat bread without washing his hands, or that he will eat at all without a blessing, if you give him and don't tell him that he needs to wash his hands and bless. . . With regards to what my dear grandson wrote, that someone who habitually does not wash his hands or bless is considered under duress because he does not know; even a child captured by the gentiles . . . is liable to bring a sacrifice, and therefore it is not considered duress. . . . It is possible that this case is different. Perhaps, when a person performs a transgression without knowledge that it is forbidden, the law of “[do not put a stumbling block] in front of a blind person” does not apply. . . For a Jew that was captured by gentiles when he was a child, if he knew that it was forbidden, it is possible that he would not do it. Therefore, when he transgresses without knowledge of the prohibition it is treated as an accidental transgression. Thus it is possible that he is considered to be under duress, and there is no prohibition of “in front of the blind.” . . . Therefore, it is appropriate to say that with regards to someone who is under duress, because of the habit caused by lack of knowledge, there is no prohibition of “in front of the blind,” and one should not avoid giving him anything when there is a need." [Translation by Rabbi Steve Greenberg]