history

I'm not sure about this particular conflict or the role religion played in it but if religion played as significant of a role as you say it did, it would be an isolated incidence.

Concerning the Balkans and Asia Minor, it wasn't an isolated incidence but widespread practice. It took place in Greece, Albania, Yugoslavia (then Serbia), Bulgaria and so on. There was even an army (Janissaries) made of children taken by force from Christian families, while those who changed their religion by their own will usually remained in their native land as part of the occupation forces.

I don't think this video makes the case for this at all. I am not convinced this religious angle played as much of a role as you say it did.

The video talks about a certain category of (European) slaves, who were captured mostly by pirate raids. That is different than the slaves captured by the regular army as in Chios massacre.

So in the context of certain areas, yes, it was a matter of Muslims treating Christians as slaves, and perhaps someone can tell us if the situation was similar in Spain (before the Ottoman era).

Concerning the way poor workers are treated in rich Arabian countries, many people wonder why "immigrants" demand to become a Muslim minority (or rather a majority) in European countries instead of preferring countries of the same faith. And countries like Qatar fund camps and mosques for those "immigrants" instead of accepting them in their land.