The Kubrick example at the bottom is a perfect demonstration of the confusion around this "rule". Cutting from a two-shot one side to a two-shot the other isn't remotely confusing and can be an excellent choice. Watch out for it and you'll see it happens quite often, in scenes that aren't anything to do with representing madness.
You'll notice when he cuts into the CU at the end, he doesn't break the line - at that point it *would* be confusing (not to mention visually ugly) so he doesn't do it.
Not to rain on your parade but this wasn't actually intended to be the opening scene. The Blu-Ray commentary makes that clear. The famous credits sequence wasn't going to be used either, but they ran out of money for the intended one (which is also why the opening scene changed). Last interesting change with Se7en - it wasn't intended to be rain-washed either but Fincher had no choice because of the weather on the first day's shooting. Yet the relentless rain becomes not only an awesome feature of the film's vision, it also becomes a great metaphor with the final journey into the blazing light of the desert. If Se7en shows you anything, it's how a great director can take problems during a shoot and turn them into gold.