Adoption is the better choice for both parties.
I think you perhaps missed the broader point though.
If you're raising children as servants to take care of you when you're old, then yes, self-interest is a good reason to keep them around. They will also likely act in their own self-interest and ditch you.
Otherwise, raising a child requires a great deal of self-sacrifice with absolutely no guarantee that you'll even get the satisfaction of a job well done. It's a total crap shoot and even the emotional return on your investment is likely to be poor.
Acting only in your own self-interest is a good way to stay single and childless though. At least you'd have plenty of time to read Ayn Rand.