Generally speaking, it is best in ANY legal document to be specific and direct, so that there are no questions that need to be brought before a Judge to interpret.  I see no problem with being brief as to your moral convictions.  But if that portion is going to have to be interpreted by others in order to determine what you do and do not want done then you are really leaving the decisions up to some one or some others rather than having made the decision yourself ahead of time.  I would speak with an attorney that does estate planning to make sure that the forms you are reading on line comply with your state law as well.  It is wise of you to think ahead.  Good luck.