I can't disagree with this more. As I said in the other thread, it's a physics issue. When someone receives a fastpass, they must go somewhere. They can get in the standby line, where the wait is now much longer than it would be without a fastpass system - because it has to accommodate a certain amount of fastpass riders per hour. Or they can get in line somewhere else - and this other line is now longer than it would be without a fastpass system - because a certain number of other people holding fastpasses for ride X (and rides Y, Z and W) are standing in front of you and without the fastpass system, they'd be in that ride X's line.
The time you save not waiting in the full line for the fastpass attraction will be spent waiting in longer lines for everything else in the park (unless you fall into the very small subset of people who only ride fastpass and zero-wait attractions).
You would be correct if people used 100% of the time waiting in lines or riding attractions, but that's not the case. We would all be surprised at how inefficiently people utilize the Fastpass system. Often times it's not even a lack of understanding of the system, but rather it's a desire not to backtrack - which is probably the crux of your argument.
It's a fair point to say that people often waste time backtracking as a result of the fastpass system and as such, it is inefficient. That argument, I would buy to a certain extent, but as I've said - I'm sure there's a cut off point for the number of attractions you can experience without the existence of the Fastpass system vs. a world where Fastpass exists. Disney has hinted that they want people to experience 10 attractions over a full day, and Fastpass aids in doing that - the biggest problem isn't the time wasted in longer standby lines, but rather the time spend backtracking.
With all that said, you can't argue that if are utilizing a system more efficiently than the average person, then you will be able to accomplish more than the average person under the guidelines of that system. For that reason, if you can utilize Fastpass more efficiently than the average person in the park - it will save you time compared to a system where Fastpass didn't exist. The average level of efficiency in touring is equal with Fastpass being employed, and without Fastpass being employed when measured in total time spent waiting in line.