Why? In my understanding the overton window is a sliding frame on an axis, so it makes no statement about the axis, only about the position on the axis.
> And to clarify, the main point of the article is that in Japan politics is not organised around how people stand on these moral questions, not that these debates don't happen.
Yes, that is what I have understood from the text, too. I find it hard to believe that there is no ideological consistency there (how are people able to make moral decisions without them, i.e. integrate their behaviour with their sense of identity?), though just as in the west the ideology and the actual political practice can obviously differ widely.
I guess it's a technical and semantic objection: A (one dimensional) window by necessity has two endpoints, and "pole" is a word that defines a point. Your use of pole is however more in the sense of direction rather than endpoint; an axis is a direction and as such can be defined by any two points along it and no set of points have such a privileged position that they warrant the label "pole".
> I find it hard to believe that there is no ideological consistency
Again, it's a statement about how parties are organised and not about how people in general believe the world works. Though I suppose this circumstance also implies there is a fairly dominant agreement on the essentials of the world-view.
And to clarify, the main point of the article is that in Japan politics is not organised around how people stand on these moral questions, not that these debates don't happen. The article does not, for example, make the claim that in Japanese criminal politics there isn't a debate between redemption and retribution but rather that positions of the individual politicians in this debate will not correlate very much with their party allegiance.