A lot of statistics have been introduced on this thread, and several good logical points have been made. The question's a sticky one, no doubt about it, and I certainly don't know what the answer is. Unless someone out there is an illegal immigrant though, we've not heard from the group with the biggest stake in all of this.
Not that it will change any minds, but here's what they all risk, and what 500 or so of them experienced this year alone. Not for the squeamish...
In 1906, W.J. McGee published an account of the experiences of Pablo Valencia, a forty-year-old sailor-turned-prospector, who survived almost seven days in the Arizona desert without water....
Saliva becomes thick and foul-tasting; the tongue clings irritatingly to the teeth and the roof of the mouth .... A lump seems to form in the throat ... severe pain is felt in the head and neck. The face feels full due to the shrinking of the skin. Hearing is affected, and many people begin to hallucinate... [then come] the agonies of a mouth that has ceased to generate saliva. The tongue hardens into what McGee describes as "a senseless weight, swinging on the still-soft root and striking foreignly against the teeth." Speech becomes impossible, although sufferers have been known to moan and bellow.
Next is the "blood sweats" phase, involving "a progressive mummification of the initially living body." The tongue swells to such proportions that it squeezes past the jaws. The eyelids crack and the eyeballs begin to weep tears of blood. The throat is so swollen that breathing becomes difficult, creating an incongruous yet terrifying
sense of drowning.
Finally ... there is living death, the state into which Pablo Valencia had entered when McGee discovered him on a desert trail, crawling on his hands and knees: "His lips had disappeared as if amputated, leaving low edges of blackened tissue; his teeth and gums projected like those of a skinned animal, but the flesh was black and dry as a hank of jerky; his nose was withered and shrunken to half its length, and the nostril-lining showing black; his eyes were set in a winkless stare, with surrounding skin so contracted as to expose the conjunctiva, itself as black as the gums...; his skin [had] generally turned a ghastly purplish yet ashen gray, with great livid blotches and streaks; his lower legs and feet ... were torn and scratched by contact with thorns and sharp rocks, yet even the freshest cuts were so many scratches in dry leather, without trace of blood" (Philbrick, 126-128).