Historical precedent and agreement make the choice no less arbitrary - 0 degrees could have been anywhere, there is no technical reason that Greenwich was chosen.
Choosing Greenwich as 0-longitude meant that the International Date Line would be located in the middle of the Pacific Ocean, avoiding a situation where it could be two dates in the same country simultaneously.
That fails to make the first choice any less arbitrary - the choice was made to line up with existing sea charts - which of course used the Greenwich as 0 - but Greenwich as 0 was an arbitrary choice in the first place - not all arbitrary choices are bad ones, that was the crux of my argument in the first place.
