Switched at birth

Suppose I have a 14-year-old son named Jeremy. And he's a really great kid. Then, one fine day, another 14-year-old boy by the name of Josh turns up at my doorstep, claiming to be my real son. He says he and Jeremy were switched at birth. Jeremy's mother found out that her baby had a genetic defect, but it was too late for an abortion. His mother was a nurse, so she and her husband conspired to swap Jeremy for a heathy kid in the same maternity ward. They didn't want to raise a special-needs child. 

I have to admit that Josh bears an undeniable family resemblance, whereas Jeremy never did look much like my wife or me. We do a DNA test and confirm that Josh is my long-lost biological son. As it turned out, Jeremy never had a genetic defect. The test gave a false positive. 

If I could step into the time machine, would I trade Jeremy for Josh? I'm too conflicted to answer that question. On the one hand I bitterly regret the lost years with Josh. In effect, having my son kidnaped at birth. I yearn for the years we lost. All things being equal, I wish that could be undone.

But it's not that simple. I raised Jeremy for the first 14 years of his life. The belated discovery that he's not my biological son doesn't change my feelings about him. The paternal instinct is broader than biological offspring. That's why many men volunteer to coach junior high and high school sports. They like to mentor young guys. It's a natural extension of the paternal instinct.

I can't stamp "return to sender" on Jeremy's forehead. Although it's not metaphysically too late to turn back the clock, thanks to the time-machine, it's psychologically too late. And since his biological parents didn't want him, what kind of parents would they be to him? I can't do that to him. In all likelihood, he was better off with me. And I can't just tear him out of my heart. 

Conversely, maybe Josh would be a worse son than Jeremy. Kids can be a great disappointment. Sometimes they don't turn out the way you hope. Then again, for all I know, maybe the alternate timeline would be just as good. 

The point of this thought-experiment is that I don't think there's one best possible world. Indeed, I don't think there's one best possible life. 

Moreover, short-term evils can be a source of long-term goods. Goods that never happen in a perfect world.