The only way to justify that stuff is NK doesn't want to kill anyone or at least doesn't want to kill Jon, he was just toying with them to get his dragon. They showed him throwing spears into flying dragons ffs, he could have done the same into Jon's (or anyone's) face while he was standing still. He and his generals made absolutely no attempt to kill anyone except that one that Jon ambushed. It's also a bit of a nonsense that they all can't swim since some are basically still humans and the white walkers are clearly as able bodied as any man. So I'm hoping the NK isn't 100% evil, just misunderstood, like Mance Rayder who was supposedly the enemy of civilisation. After all, if you look at what the NK has actually done, is it any worse than what Tywin, Cersei etc. have done for power? Or even Dany? Building an army to take over, massacring opposing armies in the meantime? And they're doing something with those swirly symbols, maybe something religious? We've already seen religious people burn children and make sacrifices, so maybe they're no more evil than evil humans? I wish they'd revealed more backstory this season I don't like the convenient idea that it's just this zombie horde with no purpose other than to kill people.