There's probably a legitimate point to be made that countries typically spend a large amount of money during an individual's formative years that they don't pay

There's probably a legitimate point to be made that countries typically spend a large amount of money during an individual's formative years that they don't pay back until they've spent a significant length of time working, so they have in essence pre-used a lot of those services. I wouldn't personally advocate that stance - I think it's problematic with respect to consent - but I can see that in the case of extremely high emigration rate the viewpoint might be very tempting.