As for the human temperature, the human thermometers measure to tenths of a degree; anything under 37.4 is considered a sub-fever, indicating that something is wrong but not yet severe, over 38 things are serious, over 39 drastic measures are required, at close to 42 the brain starts dieing. On the other hand, anything under 37 is considered normal, down to about 36; less than that might mean another set of problems entirely. Doctors are not impeded in their abilities to diagnose diseases by the Celsius scale. If they thought so, the precision of the thermometer would just go to two decimal points, but since nobody makes one of those for human use I presume that the doctors consider it unnecessary. I would rather defer to their expertise than to yours.
I find it extremely shirt-sighted the claim that the metric system is impractical, when in fact it is being used, every day, by the vast majority of the people on earth. It's basically denial-ism. The imperial system is not unusable, it's just different, but the claims of it being somehow better are just wishful thinking. Again, this is my opinion, but I bet there are more who share it than the ones who share yours.