No, they're not. Planck units are most certainly not arbitrary.
Also 32 and 212 are far more arbitrary than 0 and 100.
And failing that, outside of the specific unit of scale, Kelvin certainly isn't arbitrary.
To be fair to the side that we do use and often abuse arbitrary units though, people have created some utterly stupid misconceptions. One of the worst imo- the "fake nerd" T-shirt:
"Resistance is futile if < 1 ohm"