White walkers as far as humanity is concerned (all of it), are bad especially right now when there's clearly a broken power balance benefitting the white walkers, so assuming jon becomes a white walker he should contribute for that imbalance and might even become a antagobist for his own family members which isnt exactly pleasing but we all know Martin can turn jon into a edgelord if he wants to, lady stoneheart is a prime example, of negative character development been given to a GoT character after ressurection (well in GoT standards it's development that is required for the environment the characters are in, if they dont adapt to the situation they die, which makes me think Jon can go very far in negative development if he ressurects (maybe even more than lady stoneheart)).
Still this all depends on a lot of circunstances so it's just speculation at this point, but I wouldnt surprised if Martin made Jon Snow a more villainous character after he comes back, it would match the series quite well.