I'm just enjoying all the whiny 'oh my God, how can he do this to us', 'why does Martin hate poor wittle House Stark', and 'Martin is a horrible person' crap. People are so shallow. It's called Evil Will Triumph Because Good Is Dumb--at least in the instance of House Stark.
Also, you aren't the good guy any more when you go back on your word and spurn an ally. It doesn't matter how much you apologize, you turn into a douchebag that doesn't deserve to be a king. No, it doesn't deserve the heinous vengeance that Walder Frey extracted, but it makes those fans that view Robb as a shining hero into hypocrites.
There is no good, there is no substance to honor--there is only power. That's the representation of the world in SoIaF, and the sooner people realize that, the less they'll have stupid reactions. Of course, I love laughing at said reactions, so I hope they never realize it
I'm of course not referring to reactions on this board.