Maybe I see Roberts as a centrist because he puts the Court’s legitimacy ahead of his personal politics.

To dumb it down further It's really the difference between lawful evil and neutral evil or chaotic evil. Or the difference between longtermism and shortermism.

Roberts wants ultimate outcomes that are as radically right wing as those desired by Alito. The difference is that Alito wants those outcome to occur now. Roberts wants those outcomes to happen gradually over decades. This is because Roberts is afraid of blowback; Alito is aware of this argument, but he believes that the power of the Supreme Court and the Republican Party has been consolidated so absolutely that such fears of blowback are unreasonable and illusory.

The metaphor of boiling the frog gradually over a long period Vs dropping the frog into already boiling water is apt. You place a frog into a pot of room temperature water and then gradually turn up the heat until it is boiling. This prevents the frog from jumping out of the pot, something it physically could do at any time, because it doesn't perceive the graduality of the temperature changes. Alito et al understand the wisdom of slowly boiling the frog; they just believe that the cooking pot we are using is miles deep such that it would be impossible for any frog to jump out - and that we have also chained on a heavy lid to the pot that would also prevent frogs from escaping. We are that frog, and Alito believes that the GOP has fully constructed that enormous pot and lid. Under that worldview, there is no meaningful negative consequence for SCOTUS making drastic revisionist decisions whenever they want. The decisions may radically overturn precedent, but they are nonetheless unchallengeable.

It is our job as citizens to prove Alito wrong. If we don't then our standard of living will rapidly deteriorate even more radically than it already has since 1981. SCOTUS will remake the United States completely, and make it an absolute dictatorship of the billionaire. That must be opposed