He's not safe! It's a game of chicken. Walt is betting that Gus requires a 99.9% pure product to make X million a year. But what if Gus, a careful mofo if ever there was one, decides that Walt, Jesse, and their craziness are not worth risking his identity and his life for. Messing around with a dumbass like Walt might cost him his X million and more. Why not get another cook and make a 90% pure product and a safe X/2 million?
And if not, how does Walt know he doesn't have 3 more Gales lined up? How does he know he doesn't have 3 copies of the lab notes and detailed video analysis of his actions in the lab?
How does he know Gus won't get capped tomorrow by the cartel on their way to him?
Walt is making assumptions and playing chicken, and no matter how safe, those assumptions are putting his family's life on the line every second of every minute of every hour of every day. And he's not changing his actions at all, but instead is digging in deeper all the time.