As much as I love the Wolves, there is one thing I criticize them for, which thank the Old Gods was corrected later. Why didn't they exterminate House Bolton a long time ago? In the past, the Starks wiped out Houses Greenwood, Amber, Towers, Frost, Greystark etc. Why were the Boltons spared? None of the previously mentioned houses (as far as anyone knows) were as crual and ruthless as the Boltons, or for all we know, they may have been wiped out by less benevolent Kings in the North.
But House Stark's insistance for the Boltons to bend the knee is one of the minor factors that lead to the Red Wedding. I'm just glad that House Stark ultimatly bounced back and ended the Bolton line.