Plessy v. Ferguson was settled law. Until it wasn't. And it was rightly overturned after decades of injustice. I bet there were many in the 50s who cried about settled law. Basically, the stare decisis argument is very limited, and the best anyone can hope for is that stare decisis is time-limited. Plessy lasted 64 years, while Roe lasted 50. So stare decisis seems to mean "for a few decades", which I think is fair.
Stare decisis is neutral as to the content of court decisions. It can be used to sustain rightly and badly decided rulings for decades. And the court can ultimately overturn its past decisions rightly and wrongly. They can fail in the past, they can fail in the present, and they can fail in the future.