First, I should note that I 100% agree.

However, as the highways have become more crowded, it has become less practical to actually adhere to this.

If I'm going 70MPH (the prevailing speed on the NYS highways where the legal speed limit is 65MPH tends to be somewhere between 70 and 78MPH), and there are a half-dozen cars going 60MPH in the right lane, with just barely enough room between them to safely get in (ie, there's sufficient stopping room between the rear car and me, and between me and the front car), then technically I could pass the first car, pull back into the right lane, pull almost immediately back into the left lane to pass the next car, and repeat several more times. But that's not merely tedious, it's dangerous.

It's even worse when instead of a half-dozen regular cars going 60MPH, it's three tractor-trailers. Particularly since "safe distance" for them is much longer due to visibility issues.

...And, of course, sometimes when I'm doing this, some yahoo going 80MPH will zip up behind me, pass me on the right (completely ignoring the aforementioned safe distances) and then zip back into the left lane to careen onwards.