Stare decisis is critically important, but when it comes to substantive law the fact is that historically decisions don't have staying power unless there's some internalization of the underlying legal logic. Liberal justices walked away from Douglas' phrasing almost immediately and were never able to replace it with anything.
I never had a problem with penumbras. It's as apt a description as anyone could conjure to refer to positive rights which exist by implication. And in fact usage of that term goes back to jurists far more esteemed than Douglas. Conservatives have long tried to use the 10th Amendment for similar effect, but that likewise has failed, and frankly as an analytic device "penumbras" works much better.
I used to think Kennedy's "dignity" reasoning in Obergefell v. Hodges was awkward, but upon closer inspection of broader legal theory he's actually drawing upon a vein of jurisprudence that could become a cornerstone of American legal theory in this area. It's much more well developed outside the U.S., but that doesn't mean it's not consonant with American jurisprudence. Yet I haven't seen many law review articles, let alone case decisions, try to further develop this principle. I think like penumbras, liberal jurists are inclined to roll their eyes at it, even though they haven't yet got to the point where they literally roll their eyes at it. I suspect Hodges will fall quickly, unless Gorsuch is able to refashion a theory based on sex discrimination much like he did for Title VII in Bostock v. Clayton County. (But that's a stretch as Gorsuch claimed to be using a plain text approach to statutory interpretation.)
Thing is, we have the constitutional amendment process for a reason - it is supposed to be a living document, true enough, but it's supposed to be updated through political process, not judicial. The problem, of course, is that the bar for amendments is so high that they become impossible in practice; but it's also impossible to fix that without an amendment. Thus, so long as enough political forces believe that the status quo is preferable to other options, it'll remain that way, and we'll see increasingly contorted Supreme Court decisions to reach goals of whatever party controls it at any given moment.
That leads to another problem, which is that SCOTUS, and the system as a whole, rapidly lose legitimacy. At this point, it already doesn't matter much whether any given decision is legally sound or not - it will be supported or opposed consistently along partisan political lines. The same people will castigate the judges for "inventing" rights in one decision, then blame them for not buying into the rights "invented" by other judges. I don't know how much longer we have left, but this passage from Federalist Papers (#22) comes to mind:
"... two thirds of the people of America could not long be persuaded, upon the credit of artificial distinctions and syllogistic subtleties, to submit their interests to the management and disposal of one third."