Zero requires knowledge of the unit for it to be meaningful. There are lots of examples (like the one I gave) that are misleading without knowledge of the units measures and it only takes one example to disprove the assertion that zero doesn't need units.
Even using one of your examples.
0 feet = 0 miles
If a contractor is asked the length of road paved to the nearest mile that afternoon and, assuming only 1000 ft were laid, he would correctly answer if he said 0 miles. But in no way does that mean 0 feet. If he said 0% or 0 elephants he would probably be put in an asylum.
Zero as a number is no different from any other. It is just one integer in a continuous integer range from - infinity to + infinity. When they count down to a shuttle launch, 3, ,2, 1, 0 doesn't switch from meaning seconds to lift off to meaning elephants just because 0 is used.
