That's the thing about Stannis. He USED to be a guy who was "I must follow the law no matter the cost" but has become the guy who keep compromising his principles for his ambitions.
Normally, a guy willing to compromise personal beliefs for results wouldn't be such a bad thing but for Stannis it's pretty awful since he doesn't have any real restraints anymore.
It's a nice subtly for a series that's supposedly dark and cynical: The guys who are amoral (Tywin) and violate their own principles (Stannis) may seem to have the upper hand but eventually it blows up in their faces (Tywin suffering patricide, Stannis' usage of black magic ended up giving the Lannisters a huge advantage).
The honorable people like Ned may have gotten killed off early on, but they had such an impact on people in their lifetimes DUE to their inherent goodness and honor that their legacies will live on much longer. Ned has been mentioned with fondness in every single volume by a variety of people, whereas most everyone forgot about Robert after he died and I can't imagine anyone will think fondly of Tywin or be inspired by his memory.