The metric system is entirely arbitrary. It's just been recently back-filled to make it seem consistent and reasonable.
Look up the original definition of the meter, kilometer, etc. "The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1799, it was redefined in terms of a prototype metre bar (the actual bar used was changed in 1889 and 1927). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted."
How is something that is based on the then calculated distance from the equator to the north pole. Why do I say calculated? Well, because: "One of the earliest expeditions to set out with the explicit intention of reaching the North Pole was that of British naval officer William Edward Parry, who in 1827" https://en.wikipedia.org/wiki/North_Pole#Pre-1900... No one had been there yet. So they didn't lay a tape measure down. You couldn't actually even do that. And the earth isn't even flat anywhere so you're measuring an idealized object. Even more arbitrary.
But ignore that... ITS BASED ON THE CIRCUMFERENCE OF THE EARTH... how is that NOT arbitrary? Well it is. That's why all of the new definitions of metric things are being redefined to be as close to absolute constants as they can be: "The metre is defined as the distance travelled by light in a vacuum in 1/299 792 458 seconds."
But that's still really arbitrary because it comes from the circumference of the earth.
And your boiling point and freezing points are also arbitrary because it depends on the altitude you live at. Sure it's at sea level for these numbers... but who lives at sea level? http://www.npr.org/templates/story/story.php?storyId=9162438 looks like 1/3rd to 1/2 (max). Maybe way less.
So the Fahrenheit argument is "the numbers that are generally useful to people for air temperature are those that exist in human inhabited or are generally hospitable", eg 0 (pretty cold) to (100) pretty hot with specialized areas knowing more about their end of the spectrum (minnesota, riyadh).
Your celsius argument means is that you care about temperatures over 100 (or 140) F up to 212F, or 37.7778 C up to 100C. I really doubt you care actually. You could just have a gague labelled "beef, pork, chicken, black tea, green tea, boiling" and be totally fine. Actually boiling doesn't even matter, it's pretty obivious when things are boiling and since it's a state change it's a very stable temperature.
It's valid that it would make things easier if the US was on the metric system. It would be valid to say that india shouldn't go 30 minutes off of the hour to have a solo time zone, because that makes time zones easier, same for indiana (if they still do that).
But don't pretend the metric measurements are any less arbitrary than the imperial ones. That's a very earth centric point of view. We should be on galactic measurements by now. You should see how much news.zcombinator.g out at alpha centauri is complaining about the metric system.