"Civilization" is ill-defined anyway. What's certain is that long before they embraced Christianity in a form other European Christians would recognize as such, they admired Europe. Europe had great buildings, castles, cathedrals, palaces, walled cities, places of learning, markets, unlike anything in Scandinavia at the time. They wanted those things. And they could only get so far as pirates and slavers.

Interesting that you see it as a higher ethics to be OK with only enslaving non christians, because I really did not mean anything like that, as I do not see it as a higher ethic.

And like the other commenter pointed out, civilization is ill defined. I was mainly using it here from the christian point of view, where pagans are not civilized by definition. Not that the norse had not a complex society themself.