Yes, I took it over here because I felt it was side-tracking the original thread too much, but also because it is a natural part of talking about what love is.
Many things would seem a reasonable reason for killing, different things for different people. Like the one you mention. Others might feel that people who commit blasfemi should be killed, people who deal in drugs, people who rape, people who abuse animals, people who construct more an more refined weapons, some politicians, and so on and so on. To each that particular reason is 'justifiable homicide'.
But those are private reasons. What I wonder is why, in some places, there is also a legal idea that it is justified to kill a cheating spouse - of all the reasons people might have.
And I wonder why, and waht is has to do with 'passion'? What passion is it we are talking about?