Okay, from the top. I didn't suggest anything.
Drivers should use main beam on unlit (or lit) roads when there is no traffic approaching. This is what main beam is designed for, this is why it exists.
When traffic approaches, you flick back to dipped beam, to avoid dazzling the oncoming driver.
On any car, Mk1 Focus or otherwise, the action of flicking the stalk cancels the dipped filament and illuminates the main beam filament. But this is virtually instantaneous - in fact in many switches the main beam element comes on fractionally before the dip extinguishes. But even if that isn't the case, we are talking hundredths if not thousandths of a second between switches. You certainly don't get 50 yards or so with no light whatsoever, in any car!
You've not spotted his point because it's so daft.
He is actually saying if you use full beam, you get a huge black hole over the entire area the dipped beam used to shine, where you cannot see anything anymore. He beleives this happens and is dangerous.