The Ninth Amendment makes it extremely clear that the list is not exhaustive. There is no originalist or textualist reading that can make "these are the only rights you have" valid.
But whether the SCOTUS judges should write wholesale changes to the scope of the Constitution or rights that drift away from the original intent? That certainly is a matter for debate and thinking about implications.
There is a mechanism for changing the Constitution, amendments. Why should certain topics, if they rise to the level of "should have been an amendment passed by the people", be imposed by the justices?
What if the Constitution envisions that judges should interpret ambiguities at the margin, and not create whole new rights that drift from the fundamental codebase, if you will?
And then on top of that, if some new right involves significant social questions and implications, why should 9 justices (legal professionals) be the ones to say what the answer is?
As you said, these are open for adjustment. But whether the rights you seek should be created by justices versus the democratic process I think I differ with. Or at least, I see the logic of the more conservative approach to.
The law is already a high bar. The process is designed to favor inaction. A dedicated minority can prevent law from passage -- and can do so solely for political reasons, regardless of their personal feelings or those of their constituents. To pass a law requires control of the House and the Senate (by a filibuster-proof margin) and the Presidency, at the same time. And an amendment is even higher than that.
The Supreme Court should be able to shortcut that by recognizing that the 9th Amendment explicitly forbids a reading of "you don't have this right if James Madison didn't give it to you". When they make that claim, the entire process is cast in doubt.
I would vastly rather see the Congress pass these rights. But when the Congress has cemented a Supreme Court dedicated to ensuring that you gain no rights, and is further willing to use any minority advantage to guarantee that it can't be done by law, then the Constitution really is a suicide pact.
The Constitution draws its concept of rights from philosophy surrounding natural rights. If you're not using the word in that context you're talking about something else.