1. Its subject must be a grave (or serious) matter.
2. It must be committed with full knowledge, both of the sin and of the gravity of the offense (no one is considered ignorant of the principles of the moral law, which are inborn as part of human knowledge, but these principles can be misunderstood in a particular context).
3. It must be committed with deliberate and complete consent, enough for it to have been a personal decision to commit the sin.
The question is about point 2. While Hitchens knew that it would be morally unacceptable according to Catholic doctrine, he considered writing the book as the right thing to do according to his own moral standard, so he would not be doing something he considered as a gravely wrong thing to do. Similarly for other people who live according to what they sincerely believe: they are not committing actions with full knowledge that the actions are the wrong thing to do.
It does leave room for interpretation, and can be argued both ways, but I do not wish to be drawn further into a religious discussion.
http://en.wikipedia.org/wiki/Mortal_sin
1. Its subject must be a grave (or serious) matter.
2. It must be committed with full knowledge, both of the sin and of the gravity of the offense (no one is considered ignorant of the principles of the moral law, which are inborn as part of human knowledge, but these principles can be misunderstood in a particular context).
3. It must be committed with deliberate and complete consent, enough for it to have been a personal decision to commit the sin.
The question is about point 2. While Hitchens knew that it would be morally unacceptable according to Catholic doctrine, he considered writing the book as the right thing to do according to his own moral standard, so he would not be doing something he considered as a gravely wrong thing to do. Similarly for other people who live according to what they sincerely believe: they are not committing actions with full knowledge that the actions are the wrong thing to do.
It does leave room for interpretation, and can be argued both ways, but I do not wish to be drawn further into a religious discussion.