The fact that a function can perform asynchronous operations matters to me and I want it reflected in the type system. I want to design my system on such a way that the asynchronous parts are kept where they belong, and I want the type system's help in doing that. "May perform asynchronous operations" is a property a calling function inherits from its callee and it is correctly modelled as such. I don't want to call functions that I don't know this about.

Now you can make an argument that you don't want to design your code this way and that's great if you have another way to think about it all that leads to code that can be maintained and reasoned about equally well (or more so). But calling the classes of functions red and blue and pretending the distinction has no more meaning than that is not such an argument. It's empty nonsense.

"We" don't all agree on this.