when it comes to killing innocents, raping women, or abusing children, then morality is an universal absolute-
you. do. not. do. it.
and morality is only subjective in the minds of the subhumans who commit the offences that the rest of the world find abhorrent.
as to the question of whether a pre-emptive strike can be morally justified, then yes, it can, provided the justification is a real and present danger, and not an imaginary threat.
after all, who wants to enter an ass-kicking contest with a one-legged man....?
In ancient Greece a warrior took his boy lover with him on the war campaign because it was considered not right to take his wife or female slaves incase he lost the battle. ( I don't have a citation for this I'm just remembering this from my philosophical ethics course back in my college days)
In some Muslim cultures it's ok to kill your wife if you want.
There was a desert code in the middle east that often gave you the right to kill another person under certain kinds of infractions.
In many army's you were expected to take young slaves after conquering a city and do with them as you will.
In our culture make permiscuity is almost hailed as studly trait, while in others it's a capital offense.
I have heard of one isolated practice on some remote island that is so vial I cannot even mention it here, yet it's a matter of fact part of their culture.
I wrote a huge paper on female genetal mutilation and it's horrors once, yet in practicing cultures it's considered and honor.
The list is endless. Human codes of morality vary from culture to culture and from extreme to extreme. Judging another person by the standards of your own culture is silly. You are probably doing something that is vial to them. You may not understand it, but that is the truth of the matter. There is no universal prescriptive morality. Each culture has its own, though with the evolving global culture, it is changing thank goodness.