I don't think anybody is arguing that Cantonese and Mandarin doesn't have common underpinnings, but rather that they are not mutually intelligible. French and

I don't think anybody is arguing that Cantonese and Mandarin doesn't have common underpinnings, but rather that they are not mutually intelligible. French and Spanish, as romance languages, have a lot in common but they are separate languages. Writing Cantonese in standard written Chinese is similar to asking Spanish speakers not to write phonetically, but to rather write in French.