I know some have suggested that Robb's will makes Jon his heir and King of the North but I wonder why the show didn't make Sansa the focal point of the north as the Lady of Winterfell. And when Dany's message comes, Jon goes as emissary for his sister, protecting her from a dangerous situation. Then him joining her isn't so much of a stuff you to everyone back north.
As others have said, everything he has done since leaving Winterfell has been incredibly selfish and stupid. I know that show's have to work a certain way ie the lead character goes charging into battle but him constantly putting himself in dangerous situations, being shown to leave Sansa alone and with no communication as to what he is doing and throwing away those people's loyalties at the drop of a hat makes him look pretty dickish.
They could have made this slightly more palatable by showing Jon seeing and believing that Dany would be a better ruler for Westeros. At least that would imply he is doing everything for the sake of his people and not as others have said for a pretty face.