Mourning Someone Against Religion
Question
This one sit Shiva for a person who was against religion
Answer
Shalom!
Thank you for your question.
As a general rule, even a Jew who sins is to be mourned.
However, according to the letter of the law, those who live a lifestyle of sin are not to be mourned. An example of this is one who never kept Shabbat or one who was married to a non-Jew. So too, one who left Judaism and practiced a different religion is not to be mourned.
Nevertheless, many authorities rule that one who was brought up without proper religious direction, known as a “tinok shenishba” is to be mourned even though he/she may have sinned because they could not be expected to know better. Common custom is in accordance with this view, and we mourn the passing of almost all Jews.
Therefore, it is difficult to give a ruling on mourning someone who was “against religion” as there are many factors and considerations. Much more information is required, and it is handled on a case-by-case basis.
Source
YD 340:4; 345:5 with commentaries; Chochmat Adam 156:3; Kitzur Shulchan Aruch 201:6