People generally can't feel temperature differences that fine over their whole bodies. For purposes of weather, Celsius units are closer to what people can actually feel.
I think setting the dynamic range of 0-100 based on human extremes (see below) is fine, but I don't think this is an important point really. Both scales have to have finer granularity than "cold, medium, and hot" and they do.
Only because that's what they're used to. In other measurements, what's "normal" isn't going to be 0-100, and people are used to handling them all the time.
One comment on this before we get to your examples. You can't look at averages, because they aren't meaningful - you have to look at the range, so mean+variance+std deviations. Basically, you look at what the likely numbers that people are going to use.
- What's a fast and a slow driving speed? Is it in units of 0-100?
As a matter of fact, yes. 0 is not moving and numbers near it are slow, 100 mph is "really fast" (using the terminology from the original picture I linked). If you're measuring in km/h, you have the same problem as Celsius where the scale isn't nicely correlated to normal human activity :) I think it's merely a happy coincidence that 0-100 mph works out this way (as opposed to Fahrenheit, see below), but it sure did work out nicely.
- What's an average range for human height? Is it in units of 0-100?
Human height doesn't change all that much, and really only changes for about 20 years out of a lifespan of ~80. (Hey, notice how lifespans are also good with 0-100? 0 is really young, 100 is really old)
I guess I have to concede your point though. The scale can be arbitrary and people will get used to it. That doesn't mean that one scale itself is superior or inferior.
Fahrenheit was just retrofitted to it later to be defined by it based on 32 & 212 degrees to make the original, almost completely arbitrary scale have some logical basis. (It was originally based on chilled brine and human body temperature.)
That's exactly my point (no one figured out why Fahrenheit works out this way until you said it just now). Human body temperature being 100 on the scale sets the scale to something that humans have intrinsic experience with. Obviously not human body temperature directly, but outside weather temperature which is related to human body temperature by virtue of evolution giving us a body temperature that tolerates those outside temperatures. On the low end, Fahrenheit used a freezing point of something lower than water, probably something he considered "really cold". My point being, he set the 0-100 range of his scale to extremes that humanes were reasonably likely to encounter. Just judging by that for human use (ignoring all the other SI benefits), I think this makes it a superior scale to Celsius.