If someone gives another person $100, almost all economists agree that the recipient is better off. Hard-line neoclassical economists will say it's true by definition; the rest won't be so emphatic, but they'll confidently agree. Even happiness researchers will probably sign on; income doesn't raise income much, but the effect's still positive.
If someone gives another person the gift of life, however, I've noticed that many economists suddenly become agnostic. $100? Definitely an improvement. Being alive? Meh.
It's hard to see the logic. Why would a minor gift of cash be a clear-cut gain, but a massive gift of human capital be a question mark? In both cases, the recipient seems to have what economists call "free disposal" - a cheap, painless away of getting rid of the unwanted gift. Don't want $100? Drop it on the sidewalk. Don't want to be alive? Drop yourself on the sidewalk. As the great Epicurus wrote:
Yet much worse still is the man who says it is good not to be born, but
"once born make haste to pass the gates of Death." [Theognis, 427]
For if he says this from conviction why does he not pass away out of
life? For it is open to him to do so, if he had firmly made up his mind
to this. But if he speaks in jest, his words are idle among men who
cannot receive them.
You could object that suicide is a lot more painful than it looks. Yes, there are painless, effective ways to do away with yourself. But before you leap, you have to live with the knowledge that you're causing great pain to everyone who cares about you. If you'd never existed, you wouldn't be missed.
Once you accept this line of thinking, though, $100 could easily be a curse, too. Many people couldn't throw away $100... without feeling like idiots. And once they have the money, their standards of acceptable consumption might ratchet up so they actually need the gift to compensate.
Ultimately, though, skepticism about the value of either gift - $100 or life itself - seems implausible and forced. While it's conceivable that the recipient will wish his "benefactor" had left him alone, it's highly unlikely. As I quip in Selfish Reasons to Have More Kids, "No one asks to be born, but almost everyone would if he could." The same holds for sneaking $100 bills in stranger's pockets.