My 2 cents:
Zipperline or technical line is just a tactical application of skiing skills. Neither is a technqiue unto themselves. So I agree to argue one over the other, doesnt really make sense. Having said that, those who know can make technical assessments of a skier doing either. Often, a skier "skiing the zipperliine" will comes under scrutiny by some...while others just see awesome. The reason, different yardsticks to measure performance.
The zipperline camp, simply looks at speed, quiet upper body, knees together, and staying in the fallline. If they can achieve those things - its awesome. I know the real bump coaches look at way more then that, but the followers here....really arent.
The technical line camp, looks at the skiing skills, and assesses whether they are present or not. If so - its awesome, if not - it isnt. At least in theory....but like above, no doubt many are just dissing the zippers just out of dogma...equally BS.
Problems arise when people "dis" one tactical application over the other, simply out of beliefs, dogma, and/or ignorance. That is primarliy what is going on in this thread.
I assure you, its not hard to ski the zipperline, if you can ski the technical line and vice versa. Why do ski schools tend to favour the technical line? Simply because most mogul fields, are created by people who cant ski moguls, hence the bumps are irregularily spaced, shaped, etc, and generally just a mess....meaning there is no top to bottom zipper line...usually 3-4 turns worth at most. Hence a more versatile approach is required.
At WB there is a few zipperlines created for mogul freestyle team training - when not in use, they are roped off...because the zipper gets destroyed when people who cant ski it...try to.
As for zipperline being a "no no" in ski school world...that is BS. We encourage skiers to "mix it up" and ski the technical line, but when an opportunity arises, thrash the zipper...we want to see "fun and dynamic skiing". Chuck a helicopter in mid-run....provided you stick the landing...will only get you bonus marks. i remember years ago on my 4, one guy did just that...started technical line, hit the zipper in the middle for about 1/3 of the run...helicoptered out back into the tech line for the bottom 1/3. He got near perfect marks on his run.