Philip Pullman is wrong when he attacked the wording on the Brexit 50p coin.
The coin reads, "Peace, prosperity and friendship with all nations." Pullman said the coin "is missing an Oxford comma, and should be boycotted by all literate people".
The Oxford comma is a convention you can choose to follow or choose not to follow. The important thing is to be consistent and stick with whichever convention you choose.
'If you don't use the Oxford comma, there are rare occasions when you might use it to avoid confusion. But this instance – "Peace, prosperity and friendship with all nations" - is not one of those exceptions. It is completely correct.