First of all, the Vikings were the first group of Europeans to attempt to reach and settle the New World. That effort would culminate, centuries later, in the journeys of Columbus and the subsequent extermination of Native Americans. If “Redskins” is offensive, the name of their original would-be oppressors is even more so.
Second, the Vikings symbol is an inaccurate depiction of the people of Minnesota, who are quite diverse–only about one-third are Scandinavian. Furthermore, “Viking” is also a stereotype of Minnesota’s Scandinavians, not all of whom are descended from Vikings, and few of whom are warlike plunderers with primitive weapons.