No need to convert? What do you mean? Are you saying if I just intrinsically knew Celsius for weather I wouldn’t have to convert Celsius? Because that’s obviously true, but I’m just explaining I don’t intrinsically know Celsius in that way.
Also, even if I did get to know Celsius really well, I would still have to convert it every time someone uses Fahrenheit, which is pretty much all the time in the US.
Lastly, what do you mean, saying 0 C is “dangerously cold” and suggesting that below that temp is outside of the bounds of what is used for weather? Where I live the temperature stays below 0 C for long periods of time, never going above it.