I think the scenes of the Vikings murdering and raping innocent people are important. Ragnar doesn't rape, but this is not normal to Viking society, and even then Ragnar allows rape and slaughter because that is the way of his people. This is what they did, and it is important to be reminded that, although we like these characters, they did horrible shit to a lot of people. To put their culture in perspective, in real life there was a Viking who earned the name "Baby Lover" because he refused to murder children, which was considered weak. This was not unique to the Norse though, through most of human history brutality, murder of innocents, and rape were incredibly common in war. Murder and rape were a very regular part of these people's lives an we should remember that.