One of the things I write about in Dialect and Nationalism in China is how designating particular local languages as "dialects" has much more to do with the construction and gatekeeping of national identity than it does with sociolinguistics https://twitter.com/jeynnecool/status/1300265381240680453

Others have written more about this, but script has nothing to do with dialect/language distinction-- its mutual (un)intelligibility. But historically, the push to designate Cantonese (& other languages/fangyan) as "dialects" wasn't about linguistics; it was about nation-building

The push to designate one language as the national standard in the early 20thc was a push to prove China's modern nationhood-- to reformers, modern nations had a national language, and a lack of a national language was seen as proof of China's lack of national modernity

But China didnt yet have a national language. Reformers had to create one. They subsequently had to reframe the relationship between the chosen standard and all other Chinese languages as hierarchical: that China had one "language" and multiple "dialects"

And this had had an effect on identity. Calling Putonghua a "common language" and fangyan “dialects” implies that Putonghua can represent a unified sense of national identity and citizenship in a way that no fangyan could. That implication is baked into current propaganda today.

In other words, this hierarchy is not just about language-- it is deeply tied to a vision the PRC state today has about Chinese identity: an essentialized, homogenous identity supported by the state that blurs the distinctions between ethnicity, nation, and political loyalty.

And as James points out, framing Putonghua as the only Chinese language, thus reinforcing the PRC state as the gatekeepers of Chinese-ness, ultimately diminishes the significance of other Chinese languages and endangers them https://twitter.com/jgriffiths/status/1300287848327897088

In sum, arguments that Cantonese is "just a dialect" isn't about linguistics-- its about collective identity and cultural significance. It is meant to reinforce the hierarchy between Putonghua-- and the vision of the Chinese nation it represents-- and other Chinese languages