Because it is the only thing that has ever been mine! That was not intruded upon, taken away, held at arms length, told no, Jon Snow, this is not for you, this is for those born with their father's name.

[Oh, crap. That wasn't supposed to come out. He gets sullen, then. He had his relationship with Arya and that's gone, and now his relationship with Ygritte is gone as well.]

Highborn girls, lowborn boys. You suffered for your name and I suffered for the lack of it. And Robb died for it.