I think you're projecting your own concerns onto the author. Certainly language is not owned by anyone (which is why the French approach is stupid) and languages always evolve (as the author acknowledges early in the article). The article is not trying to change American English, it's aimed at a British audience and drawing attention to something that the author fears the British are losing by adopting American English without thinking about the consequences.

I grew up in England but live in Canada and speak quite Americanized English as a result. I've got nothing against Americans or them speaking American English and I don't think the author has either. I do agree with him however that as Brits (and as Canadians in my case) we are losing something valuable by adopting American English unthinkingly and it's worth paying a bit more attention to individually when we use language as a result.