Tricky subject–in part because much of the details get cloaked in official denials. 
 
1: Kidnappers often hold people for ransom–and I surmise that people often pay the ransom, or else kidnappers would get out of the business. So perhaps we should not be surprised that governments behave similarly. 
 
2: The Independent has a story about the long history of US/Russia (and formerly Soviet) prisoner swaps. Typically the nations have swapped spies for spies. This time the US traded an arms dealer for Griner. I have no evidence that Griner was a government agent–but then, the US government would have no reason to disclose this fact. 
 
3: Is Sumner being myopic? Perhaps Russians think that the US government incarcerates Russians solely to blackmail Russia into giving up US nationals found guilty of committing crimes in Russia. On the other hand, even if they do, does this otherwise undermine Sumner’s thesis against prisoner swaps? 
 
4: Assuming we have all the relevant info, then I tend to share Sumner’s concerns about the incentives made by prisoner swaps, although I might phrase his conclusion more harshly.
 
In the case of Griner, perhaps the prisoner swap reflected Biden’s failure to understand the incentives that such a swap would create. That would be bad. Alternatively, perhaps Biden fully understood the incentives. And that would be worse.
 
Public Choice theory suggests that government agents act with the same self-interested motives as private citizens. So maybe Biden understood that making the swap would create bad incentives–but also understood that he has difficulty energizing a young, multi-ethnic base and that freeing Griner would provide a political boost that few other policies could match. Given these understandings, maybe Biden made a clear-eyed choice to pursue that political advantage–at the expense of the welfare of any American who does or aspires to travel abroad. 
 
I am reminded of Disney selling super-passes. Because people complained about long wait times for rides at Disney parks, Disney created super-passes that–for an additional fee–let visitors jump to the head of a line. But in providing these super-pass benefits, Disney must inevitably push all OTHER visitors further back in line. In short, Disney’s super-pass policy appears to provide a remedy for customers’ problems–but the remedy operates only by making the problems worse for the great majority of customers. 

So Russia arrests a person who openly admitted to smuggling illegal drugs and received a similar sentence to others in the same boat domestically and less than her own government would have given her for the same crime but that’s bad because…well Russia lol.  The horror, the horror.   
It appears the real crime here is Russia didn’t simply execute her without trial during an “arrest” or as a “enemy combatant / collateral damage” which is the favorite tactic of the USG, instead they had the gall to simply arrest and prosecute her with a fairer trial than she would have received in the US and then put her in a prison that is safer and more humane than it’s US equivalent.  And as a bonus she’s not even considered a felon so doesn’t lose any rights, career impact, travel restrictions, etc.
Must be nice to be a rich black celebrity or a Jew as in the case of Evan.  Whereas if you are a old white guy from Texas accused of molesting your children after your wife kidnaps your children to Russia or smoking medical marijuana, Scott’s cool with that, you can rot lol.
Lets be real here, there are about two dozen US citizens in Russian prison.  There are nearly a thousand Russian citizens in US prison.  Who is kidnapping who?

Fortunately these examples of blackmail are not that important. In the end I would have made the same trade. However, the central point by Scott is accurate. What should we do? Could we be proactive and kidnap first? Then also raise the cost. For example, we could “up the ante” and announce that we will destroy territory or valuable areas for each kidnapping etc. (Of course our WNBA player was carrying illegal drugs)

But we also must admit that sometimes we really don’t know the circumstances. For example, how do we know the WSJ journalist is not a de Facto spy?

We can also announce to our own citizens that for a defined set of countries they are on their own. Then again, look at our own country. Thievery is, for all practical purposes, permitted in our own country. Arrest, release, a

Citing Hollywood movies is falling for the logical fallacy of generalization from fictional evidence. In those movies blackmail plots revolve around secrets the protagonist wants to keep (often from the government, as they may involve crimes). Kidnapping is instead an extortion plot, with blackmail just being a subset of extortion (one many libertarians want to legalize).