There is a certain bad argument for the legalization of alcohol/tobacco/drugs/abortion/prostitution/gambling/guns/etc that goes like this:
Sure, X isn't the best thing in the universe. But really, banning it has done more harm than good. After all, you can't stop people from doing it. (INSERT STATISTICS ON UNDERGROUND USE) But as long as it's illegal, people will be forced to turn to crime to do X. (INSERT SOB STORY ABOUT BACK-ALLEY X) Indeed, since X is banned, organized crime has moved in to provide X. But if X was legal, X would be far safer for everyone, user and non-user alike. It could even be taxed!
Now let's try sticking "slavery" in X.
Sure, slavery isn't the best thing in the universe. But really, banning it has done more harm than good. After all, you can't stop people from doing it. (INSERT HUMAN TRAFFICKING STATISTICS) But as long as it's illegal, people will be forced to turn to crime to buy or keep slaves. (INSERT SOB STORY ABOUT HUMAN TRAFFICKING) Indeed, since slavery is banned, organized crime has moved in to provide slaves. But if slavery was legal, slavery would be far safer for everyone, slave and owner alike. It could even be taxed!
Disgusted?
Don't talk about politics, religion, or Gozoltry.
But why is the argument bad? After all, we can agree that slavery is bad, but why the argument itself? Where did it come from?
Rather than take an existing example (with all associated feelings and arguments) let's invent an entirely new practice, which we'll call Gozoltry. You and I have never heard anything about Gozoltry, except that people are upset about it on the Internet.
Gozoltry? How about NOzoltry!
And here you see two arguments:
One goes like this:
Gozoltry is WRONG. (INSERT SOB STORY) We must stop it all costs. Even if the fight is futile, we must fight.
The other goes like this:
Gozoltry may or may not be wrong, but look, it's hard to stop. Impossible, even. And the things that the government does to stop it cause more harm than good. (INSERT SOB STORY)
Now look closely. You'll see that these two imaginary internet arguments are about different things.
One is about morality.
The other is about logistics.
We do not fight Gozoltry because it is easy, but because it is hard.
A moral obligation can be defined as "What THOU MUST DO even if IT ART INCONVENIENT." Logistics is convenience at scale, regardless of any professionals studying it. Therefore, morality must trump logistics, or it is not morality. What is right is more important than what is easy.
The Argument from Logistics relies on preventing Gozoltry to be impracticable. But even if this was true (and for all we know it might not be) it's irrelevant. Nearly every law is impractical, because if it was practical to prevent X, there would be no need for to engage the vast, ponderous machinery of the judicial system to stop it. Nor is it right to condone a practice simply because it is convenient. After all, that is essentially the argument of slave owners. If X was inconvenient, it would not have been done in the first place.
As I mentioned, the Argument from Logistics relies on Gozoltry being impossible to stamp out. But this is not the same argument as the Argument from Morality, which attacks Gozoltry directly. Two Internet arguers could spent their entire time talking past each other on this subject without success. But even if the Argument from Logistics succeeds in proving that it is impossible to stop Gozoltry--so what? Human trafficking is still around, despite every attempt to stomp that out, either.
That doesn't make slavery right. Nor that it is right to legalize slavery.
Conclusion.
As for myself, there's a few in that list at the start of which I am absolutely against. Of others I am unsure. Nonetheless, I will not be convinced by the Argument from Logistics.
How would one argue for Gozoltry? Another moral argument. Argue that it's a human right, or that there is no way whatsoever to stop it without violating human rights. That is the argument I want to hear. Not that Gozoltry is too difficult to stop.
And how would we know which of the two arguments, if both argue for morality, is right?
Only by examining the nature of Gozoltry itself.