Saying we have to take the FIRST part of something without being able to consider the LAST part of something is like saying a court has to hear a case but can make no decisions.
Get your Castro issue checked. Seriously.
He isn't even getting his criticism straight. Vattel is referring to "Mechanics" during the Industrial revolution. This was a time period when such people were regard as we today regard our Scientists and Engineers. Their knowledge has real economic and military impact, and as such they are restricted in some cases from leaving the country without permission, or working for foreign countries.
In other words, we DO follow Vattel's advice in this regard. England did as well at the time.
I know. The skills of a population are a resource of the country. A great deal of what Vattel wrote, IMHO revolved mainly around the concept of monarchies.
Not that the authorities aren't the same, but sometimes there is a huge difference as to who that authority belongs to in our Republic.
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Since your response was apparently to complex for the poster, I thought I'd try the KISS approach. ;-)