Nostromos besättning leddes av rädsla för att om de helt enkelt övergav fartyget som skulle Xenomorph framgångsrikt infektera alla besättningar som kom för att rädda Nostromo och att Weyland-Yutani skulle fortsätta med deras plan tar den till jorden där det kan orsaka ett utbrott.
Ash (i novellering ) lägger det ganska bra ut;
'I cannot say. There is a distinct possibility the alien will successfully infect the boarding party and any others it comes in contact with before they realize the magnitude of the danger it presents and can take steps to combat it. By then it may be too late.
'Thousands of years of effort have not enabled man to eradicate other parasites. He has never before encountered one this advanced. Try to imagine several billion mosquitoes functioning in intelligent consort with one another. Would mankind have a chance?
'Of course, if I am present and functional when the Nostromo arrives, I can inform the boarding party of what they may expect and how to proceed safely against it. By destroying me, you risk loosing a terrible plague on mankind.'
Även om Ripleys resonemang inte läggs ut på filmens sista skära, får vi en uppfattning om hennes motivation från det ursprungliga " Starbeast " version av manuset. Kort sagt, Alien behöver dö.
HUNTER: Blow the ship up?
ROBY: And the creature with it. We can make it back to Earth in the lifeboat.