Re: Hypothetical Dilemma: 7 Billion People will die if you don't shoot the baby in the head and eat its Bodily-Remains.
If one strips all the unnecessary "fluff" (aliens?) and the appeal to emotions (eating a baybee?) the dilemma is very simple:
you are confronted with a choice of not your doing, yet you are forced to make a selection between two possible courses of action. The two courses of action both carry negative results, but one is "worse" than the other (the harm caused by choice "A" is more than the harm caused by choice "B"). The possible choice of "non-action" carries the same consequence as the "worse" one (choice "A"). Which choice should one take? (It is funny that so many people try to "wiggle out" from such dilemmas, by stating that the problem is far-fetched, or improbable. We are faced with such choices all the time.)
The answer is obvious: choose whichever causes less harm. The Hyppocratic oath is very wise: "first, do no harm". It should be continued with: "if you must cause harm, cause as little as possible".