How often are you doing the conversion manually? It seems like the sort of thing that should happen in the presentation layer so people never see the actual Kelvin amount. If you have a system where you always use SI then it's strange the have a single exception for temperature.

Hm, is it wrong to dream of a world, where this along with other basic science, would be considered basic knowlege?

Not blaming anyone who does not know it, but I would argue for more and better science education ..