Roberts, Gorsuch, Kennedy, O'Connor and Souter all switched sides on major issues. Conservatives switch sides a lot more often, but perhaps because the court has been tilted towards Republican nominees.
When it comes down to real decisions by SCOTUS, they usually come out more moderate and narrow than you might imagine.
Among the Democrat appointees, Kagan has a more independent record than Sotomayor but came afterward.
I know there are counterexamples but my point is that there's not an obvious trend toward more partisan justices, or at least no evidence has been presented so far in this thread.
For people like me, I don't care what "side" a justice is on. The justices literally choose which cases they accept... Of course there will be some debate on them.
What I find absolutely horrid is that the courts are packed with nominees hand selected by a group of US senators who not only cannot represent the majority of the US population/citizenry, but are also actively antagonistic toward people's will to determine their own future (see obstructionism by McConnell during the Obama years).
Part of the job of the Senate is to represent the minority. They typically aren't the starting place for major legislation, but often slow down or heavily amend it.
You could argue that the minority should have no power at all, I suppose. Democrats used a similar argument to remove the judicial filibuster, which was a great idea right until they became the minority in the Senate.
That's really the big lesson that people never seem to learn about democracy: you'll be in the minority at some point, so get protections/obstacles in place while you're in the majority, or you'll regret it sooner than you think.
Sure, this is a lesson about democracy. It's a lesson about how to subvert democracy.
The math is transparent.
The filibuster is just something the senate made up. It does not exist in the constitution, so it is not a true obstacle. The R senators would have gotten rid of it anyway. It doesn't even protect the Senate "minority".
And the Senate's job is to prevent people from determining their own future. It was championed by anti-democracy activists like Alexander Hamilton. I hope it no longer exists by the time I perish.
Two sides of a conservative position.
The US, in general, does not have any non-conservative judiciary. Stare decisis by itself ensures that there is a strong conservative streak in the available pool of jurists. So yes, the Supreme court has center-left (Sotomayor), centrist (Breyer, Kagan), center-right(Roberts, Kavanaugh, Gorsuch), and reactionaries (Alito and Thomas), but nobody as far "left" as it has "right".
Historically, for example, William O. Douglas was about as left as the court has gotten, and he was more in favor of environmentalism and ending the Vietnam war than really aggressive left wing concepts.
Now you're bringing up a different claim, which is that the two major parties don't really represent a variety of ideas. That's a fine claim to make, but it doesn't contradict my point.
The other major shift is actually more along the axis of social libertarian vs authoritarian, which is not as clearly divided as "republican vs democrat", especially considering the late RBG was clearly an authoritarian in some respects, despite being fairly left of center.
Taking any of this as evidence that the court is non-partisan is pretty incorrect: They're consistently partisan in clearly obvious ways, even controlling for other issues.
Are any of them arguing for an ethnostate? For shipping non-whites "back to where they came from"? For re-establishing anti-miscegenation laws?
Your perspective is absurd. Of course the court has a left wing. It's just not radical enough for your liking and, similarly, the court's right wing isn't radical enough for David Duke's liking.
Don't kid yourself. This is exactly what they're after. Another couple of elections of the likes of Trump and they may get it.
The only debate among conservatives is over whether they should be overtly racist, like Trump, or covertly racist, like his predecessors.
If they get enough power, the velvet glove will slip from the iron fist.