Apparently sacrificing a kinsman in a Great Blot gets you the kinslayer tag.

I did it anyway - by that stage it was the only way to deal with the annoyance of elective gavelkind.

Seriously, that must be the worse of all systems of governing. Not only do all your titles get spread around by your vassals get to elect your successor from among all your brothers, son, half-brothers, uncles, cousins, nephews etc. And given you can't control the breeding or education of many of them, your vassals end up selecting some utterly useless person. The case in question was a dull character with not a single stat above 8. I managed to imprison him after he revolted for being a bad boy.

Problem is my council liked him and wouldn't allow me to strip him of titles, banish him, execute him or anything else. And he sat for a dozen years in the oubliette laughing at me with out suffering any ill effects. So a ritual sacrifice he became.

This was from my Gotland run. I've managed to claw my way to the dominate power in Scandinavia, grabbed three holy sites of the Germanic faith - only to find my fellow religious practitioners have tanked the moral authority down to 28%