Semi-serfdom

What are going to do with Paul Krugman? He writes clear and insightful articles on complex economic issues, then he gives them titles like "Serf's Up" (circa 2003):

Here's the puzzle. In Europe circa 1100, with population scarce, serfdom was useful to the ruling class. By 1300 it wasn't, and had been allowed to drift away. But after 1348 it should have been worthwhile again. Yet it wasn't effectively reimposed. There were attempts to restrain wages and limit labor mobility, as well as attempts to tax the peasants (Wat Tyler's rebellion fits into all this.) But all-out feudalism didn't return. Why?

And an even bigger question: why hasn't indentured servitude made a comeback in the modern era? Yes, I know, human rights and all that - but if it was profitable to have indentured servants in the modern world, I'm sure that Richard Scaife's think tanks would have no trouble finding justifications, and assorted Christian groups would explain why it's God's will.

Though the analogy's not perfect, we do have an institution that restrains wages and limits labor mobility. It's called an H-1B visa and though I know of no Christian groups trying to explain why it's God's will, it certainly has plenty of think tanks finding justifications for it.