Umm hmm, it's a good video. At a vantage point about 12-14" above the stock roll center, it illustrates the result of body roll and a little bushing squirm. If what you really want is for the tires to not move sideways in relation to the body, you could use a panhard rod or watts link to raise the roll center but then you're back to fighting the leaf springs again and it will get skittish over bad pavement on corners. A better solution for the car shown would be stiffer (or just new) spring bushings and more roll stiffness via swaybars or spring rate.
But anyhow, I think we're all tired of this one and I'm not going to get anywhere with it.
For the original poster, see some light-but-knowledgable discussion pro/con specific to the panhard bar issue here:
Panhard Rod on a Leaf Spring Car