Two-part question: Under what conditions does a judge look for a precedent to reach a decision? And, regarding the Supreme Court, you will hear talk of overturning a previous ruling; yet, doesn’t a past decision stand as a precedent? How easily is a past ruling overturned?
I will just mention that Brown vs. Board of Education (the school desegregation decision) overturned a decision that was nearly 60 old. Among other things they decided, on the basis of sociological evidence, that separate was inherently unequal. I don’t know what, if any part, was played by the fact that the negro schools were horribly underfunded (sometimes by worse that 5:1) compared to white schools and thus were never equal and this was going to be impossible to change.
The court has been nibbling away at Roe vs. Wade for decades and it would not surprise me to see the current court reverse it. One more Trump appointment would virtually guarantee reversal.
Technically, all it takes to overturn any precedent is for 5 justices to vote to overturn it. The New Deal court did a ton of that, suddenly finding near unlimited powers for the government under an at the time obscure clause, the interstate commerce clause.
But in the modern age, since justices have to explain their reasoning, it’s harder in practice to overturn precedent. They can’t just reverse a decision, they have to explain how the original decision was in error, or in what way it doesn’t apply. In regards to Roe, it would seem that abortion rights being guaranteed under the right to privacy is chiseled in stone. I don’t see any plausible way to explain how such a decision could be in error. But a large part of the Roe decision, the trimester requirements, those can certainly be overturned because a) they were justices making law rather than interpreting law, and b) they were arbitrary. So I could see Roe being undermined by a conservative court allowing more regulation for late term abortions.
It’s also possible to argue that medical advances have made trimester distinctions obsolete. When Roe was written, no fetus born in the second trimester had survived. Now that has happened. Such surviving preemies nearly always have long-term problems, but that’s beside the point-- at the time Roe was written, a second trimester survival seemed impossible. Now, such things as embryonic adoptions (transferring an already-implanted embryo from one uterus to another), or transfers to artificial wombs seem like things that while science fiction now, could happen some day, and the court is not outside reality to write a ruling that allows for them. The authors of Roe dealt strictly with medical science of their own present.
It’s a brave new world when court rulings have to account for what science might achieve, but advances in sciences are legitimate reasons for taking new looks at rulings.
Personally, as a person who is pro-choice, I wish that the right to privacy were the only thing Roe rested on, and not the trimester thing, but the trimester distinction is there, so it has to be dealt with. If it had stopped at the right to privacy, I wouldn’t be writing this post.
Just as another example, Oliver Wendell Holmes once famously (in Buck vs. Bell) that “three generations of imbeciles are enough.” He wrote that before anyone knew anything about the double-helix, or whether forms of “imbecility” (a legitimate medical term at the time) were heritable (he wrote before the MMR vaccine, and “three generations of imbeciles”* could easily be caused by three generations exposed to the rubella virus).
Now, Buck vs. Bell has never been officially overturned, but it’s been chipped away in the same way as R v. W, so that it has no teeth, and that’s been possible because the science was so wrong. B v. B was based pretty much only on bad science, and deserved to go the way of the Dodo. R v. W is a different animal, and like I said, I wish it had been solely based on privacy. I think it would be untouchable if it had.
*Not that Carrie Buck and her mother and daughter were necessarily imbeciles, as Stephen Jay Gould demonstrated in one of his essays. The daughter’s grades in a regular public school were entirely respectable, and Buck may have been labeled for promiscuity at a time when morals and intelligence were considered parts of the same character trait. Nevermind that Buck was probably raped…
The Holmes thing though, that was reprehensible even in his time. Many “intellectuals” were really into eugenics back then, but the dumb religious hicks that relied on the Bible thought such ideas were wrong. Sometimes the simple folks have it right.
What also strikes me about that Holmes statement is just how snarky it is. He sure was convinced of his intellectual superiority, wasn’t he? Much like many modern day liberal intellectuals.
Without derailing this thread, I would just say that I don’t think either the right or the left has any monopoly on those who are convinced of their intellectual superiority. 
True. I shouldn’t have brought ideology into it. But the point that the smartest people of the time can be badly wrong, and arrogant in their ignorance, still stands. And any precedents based on such poor reasoning should be overturned. But I suspect those opinions are pretty easy to write.