Why should we use kelvin and not as degrees kelvin?

Answer 1

The omission of "degree" indicates that it is not relative to an arbitrary reference point such as the Celsius and Fahrenheit scales, but rather an absolute unit of measure which can be manipulated algebraically (e.g. multiply by two to indicate twice the amount of heat). This is not actually the case.

Temperature (regardless of its unit) is not at all "the amount of heat" (e.g. you can increase or decrease the temperature of a gas adiabatically), so it makes no sense to say "that body has double the temperature of this one" (again, regardless of the unit used).

Temperature is not a real physical magnitude (in the sense above) so you have not to choose a "measure unit" while you have to choose a "measure scale".

This is the reason why historically the temperature units was "degrees".

Why, exactly, the IS decided to drop the "degree" for the kelvin unit... well, this I don't know.

Answer 2

It is more accurate to use "kelvin" as the unit of temperature because it is an absolute scale that starts at zero, representing the absence of thermal energy. Using "degrees Kelvin" is technically incorrect because Kelvin is already an absolute scale and does not have negative values.

Answer 3

I believe the idea is to make it similar to other units - in other words, the "kelvin" is a unit just like any other unit.