Yes, Rechtsstaatlichkeit only means that the state and its organs have to follow the law themselves. It doesn't say anything about the moral quality of the laws.

The Nazi state had to follow its own laws. They just had such laws that enabled the total lunacy that the 3rd Reich was.

All I'm saying is: If you decouple laws from morality you get a really bad time.

Ah, but legal positivism is the norm in liberal societies, and not by accident. This follows directly from the demands of liberalism which privatizes discussion of the objective real and relegates it to individual sentiment. One of the paradoxes of liberalism is that the maximization of individual liberty necessarily demotes authority and elevates power, leading to tyranny.

So any appeals to the contrary are rooted in appeals to beliefs held in parallel with the liberal doctrines of the state. When Protestants ruled the US, that means some residual (often warped) Christian sensibility, because they were able to attain that consensus. But with greater competition today, that old consensus is no longer possible. Liberalism ensures that.