In short, you don't want to use a temperature scale with an arbitrary starting point for doing calculations like this. The freezing point of water is no more or less arbitrary than the freezing point of oxygen or sodium or anything else. It's just one that's somewhat useful for everyday use. When handling calculations for multiplying temperature, you want an absolute scale like Kelvin.
0 K is like when there is 0 heat basically, while celsius isn't. Imagine a unit for distance called "goob" where 0 goobs is 100 m and 1 goob is 115 m. In that case the goob unit would behave differently than a meter when you multiply and divide because 0 of the units don't actually correspond to "nothing" in a physical sense. That's exactly how the Celsius scale is, with zero being placed somewhere arbitrarily, not at a physical zero.
absolute scales are still arbitrary. you would probably want to use a scale that measures "perceived heat" which is different than average kinetic energy
Kelvin is just our word for it, but that is the point of “no heat”. It isn’t arbitrary, there is no “negative kelvin” just like you cannot make something colder than absolute zero.
So if you take the difference between “coldest possible temp” and “average summer temp”, then slice it in half, you’re getting temperatures that would kill most life on earth.
Just to nitpick, there are negative kelvins. I don't really understand it, myself, but I know it exists due to the specifics of how temperature is defined. Negative kelvins are actually extremely hot.
that's not true. there are things that are not definitions. like my bed for instance, there are aspects that are arbitrary (my personal preferences, design choices, etc) and aspects that are not arbitrary (its physical form that exists beyond definition)