What one person calls a threat to life may not be perceived as such by another. Very subjective.
I don't know what work your "very" is supposed to do, but if one person observes a bear lumbering toward her yard and perceives in its approach a cause for alarm and a possible threat to her life, and another person observes a bear lumbering toward his yard but does
not perceive in its approach a cause for alarm and a possible threat to his life, then, since they are observing the same objective set of circumstances, their different perceptions must have an explanation. Maybe the man is an animal trainer and the approaching bear belongs to him. Maybe the man is a fool and hasn't sense enough to recognize a dangerous situation. Maybe the man is an animal rights activist and truly believes that wild animals do not pose a threat unless provoked. Maybe the man is a fur trapper and is luring the bear toward a trap. If we all agree that the approach of a bear is cause for alarm and a possible threat to life, then the differing perceptions in our hypothetical must have an explanation.
That explanation, whatever it is, accounts for their different perceptions.
To bring this hypothetical back to our topic: if two people observe the taking of a human life, and one perceives it as immoral while the other does not perceive it as immoral, or perceives it as moral or a-moral, then, since they both observe the same act, there must be an explanation for their different moral perceptions.
