I fail to see why Antonio would be expected to write in anything but American English, seeing as that he has no native dialect of English and that he has lived in America in the past and will again in the future. Obviously I have no problem with foreigners using whatever version of English they feel most comfortable with.
Obviously for Americans to type in non-American English is a hideous affectation. I have made my feelings on this very clear in the past. If Americans hate their own native culture so much that they are unwilling to use its language, they are free to find some other place to live.
It is not that I don't think Antonio should be allowed to write whichever way he likes, but it is a bit ironic that he as a European dislikes Americans writing in British English and use American English himself.
In Europe - and in the majority of the world outside of the Americas - the English version of English
is English. It is the norm among educated people and using American English signals you mainly have your knowledge of English from US pop culture. So even if Antonio has lived in America it is a bit weird for me that an intellectual French guy writes in American English (I associate European academics using American English with faux solidarity with the working class. It is the kind of thing rich Trots do).
Your intolerant view of Americans that use British English ("love it or leave it") is a bit funny since your parents immigrated from a country that uses British English. It comes off as a bit over the top.