Yeah I never understood why pagans could only raid against other religions. Pagans are supposed to be characterized by infighting, not zealotry. They can war against each other relatively easily, why can't they raid?
Like in King of Dragon Pass (a completely accurate historical account of a place which totally existed) raiding cattle from other tribes is justified under the region's religion if you can get away with it. If you can't defend your cattle, anyone else has a right to take them.
I don't really know, but I think that in real life the Norse mainly raided civilized states because they were rich targets, and unlikely to counterattack over the water.
Definitely. The usual "strategy", as far as I know, was to raid coastal settlements in Scandinavia (and the rest of the Baltic coasts) for additional slaves and trade goods as you sailed south, raid some more in the south, and then sell the slaves and loot (as well as whatever trade goods you brought from your home settlement, if any) in one of the main trading hubs before returning home (hopefully before somebody else raided your own homestead). Of course, colonisation, "taxing", and mercenary runs where a bit different, but for those raiding weren't really the goal but more the usual consequence of warfare. Except maybe the "taxing", but if they don't want to pay their taxes, what are you going to do? You need to pay for your new stronghold
somehow. So yeah, looting definitely weren't limited to non-Norse, and Scandinavians/Baltics had already been doing that style of warfare/raid/mercenary work runs for centuries (For example, by the looks of the riches and remains of and in their hill-forts, the
Island-landers seem to have been either employed extensively by the 300-400 Roman Empire... Or having extensively raided the other tribes that were). The southerners who recorded history just didn't care or bother or know about it before the overpopulation stated large-scale raiding of the their lands as well.
And yeah, raiding definitely weren't limited to pagans either. Much of the "northern crusades", or the christening of northern Europe, consisted of Christian kings and warlords repeatedly raiding the richer regions, even though the populace there had often already been converted to Christianity (again, often repeatedly). Which lead to some hilarious-in-hindsight scenarios where a foreign Christian lord would attack and the Christian local populace would seek shelter in their churches to avoid getting slaughtered, and the lord then demanding they would come out (or face death) so he could christen them. And please, if they could be so kind as to bring the church silver out with them, that would be nice, of course. And that is why so many early churches up here are built like tiny fortresses/towers - Not to defend against pagans, but to defend against other "brothers of the faith".