In this case, the portals are only moving in planes parallel to each other, so there is no stability introduced.

Portals can only move within planes parallel to each other.

SCOTUS these days can and will make up whatveer the fuck rationalization they want to justify any decision, and then tagline it with “but this only applies to this one specific scenario” to keep from locking themselves out of ruling the opposite way next time.

Last year (or earlier this year?) they ruled on a case where the event that triggered the suit was literally made up and never happened, and everyone knew it.