The Karlsbande is or used to be an Ultra fangroup. AFAIK, some members got thrown out, then a few others followed them and formed a new group. Dunno whether they're right-winged or not... let's just say, sometimes people throw around these right-wing/fascist/nazi insults too quickly IMO. They have a website, btw.:
http://www.karlsbande.de/ . If you understand German, I recommend you to read the "Über Uns" text which contains a few comments on the group splitting.
Anyway, I've discussed the Italy issue with some friends and most of them rate Boateng's walk-off as a mistake, they see it as an affront against the majority of stadium goers who paid for their tickets and just wanted to see a good match. I still can relate to what he did though, I probably would have left the field as well.