Matt Zwolinski replies to me on Peter Singer’s Drowning Child hypothetical.  Matt:

Bryan starts off by questioning whether we really have an obligation to
save the drowning child. After all, we’d praise someone who rescued a
kid in that way as a hero. So perhaps this shows that they are going above and beyond the call of duty?

This strikes me as pretty implausible.

In this case, at least, I’m hardly a lone libertarian nut.  For centuries, the Anglo-American legal tradition has explicitly denied a morally enforceable obligation to help strangers.

To have a duty to X is for it to be wrong for one not to X. And it’s
pretty clear to me that someone who walked passed the drowning child
without a very good excuse would be acting quite wrongly.

I deny Matt’s equation of a “duty to X” with “wrong to not X.”  In common sense morality, it makes perfect sense to say, “This isn’t just morally right; you have a duty to do it.”  Think “morally recommended” versus “morally required.”

We might call the person who saves the child a hero, but I
think that’s a bad way of distinguishing duty from supererogation. The
way to make that distinction is not to look at how we react to people
who do the good thing, but to look at how we react to people who fail to
do it.

We often condemn people for merely failing to do what is morally recommended, and rarely praise people for merely doing their duty.  So I think I have a better test of supererogation than Matt does.  At minimum, Matt should admit that both praise and blame are are signs of supererogation. 

But we can go further.  To jog your intuition, consider the case of the original Good Samaritan.  Almost everyone thinks him a hero.  So what did he actually do?  Luke 10:

“A man was going down from Jerusalem to Jericho, when
he was attacked by robbers. They stripped him of his clothes, beat him
and went away, leaving him half dead.
.. But a Samaritan, as he traveled, came where the man was; and when he saw him, he took pity on him. 
He went to him and bandaged his wounds, pouring on oil and wine. Then
he put the man on his own donkey, brought him to an inn and took care of
  The next day he took out two denarii
and gave them to the innkeeper. ‘Look after him,’ he said, ‘and when I
return, I will reimburse you for any extra expense you may have.’

According to the footnote, a “denarius was the usual daily wage of a day laborer.”  All the Good Samaritan did to become a timeless symbol of supererogation was (a) tend to a stranger’s wounds, (b) give him a ride on his donkey, and (c) pay two days’ wages plus a bonus.

Matt continues:

Why, oh why, does it always have to be about guns for libertarians? Yes, I know that in some ultimate sense,
every law is backed by the threat of violence. If you break the speed
limit and are sent a fine, and don’t pay it, and resist when the cops
show up at your house, and resist very effectively when they try to
physically force you into their car, then eventually they very well
might take out their gun. But that just. doesn’t. mean. that posting a
speed limit sign is the same thing as pointing a gun at you.

Methinks you doth protest too much, Matt.  Yes, posting a sign and pointing a gun aren’t “the same thing.”  But when the organization posting the sign predictably escalates to violence when anyone defies it, posting a sign and pointing a gun are morally comparable.  Think about calling “La Migra” versus physically deporting someone.  There really is little morally relevant difference.

Matt goes on:

Which leaves us with Bryan’s final, and I think strongest, point… We can live a rich,
normal life being fully committed to rescuing every single drowning
child who crosses our path. A commitment to rescue every starving child
in the world, in contrast, would consume our life.

If this line of argument works, it counts against an expansive
personal duty to rescue. But…and here’s the rub for a libertarian like
Bryan…it looks like it might actually count in favor of certain
kinds of redistributive public policies. Here’s why. The problem with
an expansive personal duty is basically one of fairness and free riding.

I’d focus on “extreme demandingness,” not fairness or free riding.  But Matt immediately adds:

Since most individuals will likely not comply with such a duty, those
who do will be left with an unreasonably large share of the overall
burden. If, on the other hand, everyone could be counted on to do their share, then each individual’s share might not be unreasonably large.

Is it “unreasonable large” to ask every middle class person on earth to permanently support several complete strangers?  That’s how the math works out if you combine plausible cutpoints with real-world data.

So here’s the takeaway. The idea that individuals have no positive
duties toward strangers is entirely implausible. And nothing in Bryan’s
argument gives us any reason to doubt that those duties are real
obligations, and in some cases even enforceable obligations.

My alternate takeaway: It’s entirely implausible that everyone on earth has a moral obligation – much less a morally enforceable obligation – to vastly surpass the generosity of the original Good Samaritan.

HT: Alex Tabarrok for reminding me about the common law and the original Good Samaritan.