Much like pirates and gangsters, Vikings are cool if you consider them from an aesthetic as opposed to moralistic perspective. Everyone has evil ancestors, but some of them were cool.

Ninjas, samurai, Native Americans in war paint, etc. It's like every culture (that has survived) has reverence for their own group.

It's one thing to find a culture fascinating, but this "aesthetic" is generally a construct of the imagination cobbled out of stereotypes.