I feel like this argument always boils down to explicit vs implicit. It tastes the same as static vs dynamic typing. Personally, I fall well into the explicit camp. I like when I can know stuff about a function without having to read its body, and the bodies of the functions it calls, and the bodies of the functions they call, and so on. And so, I like when I can see from the function signature that it returns an integer, or when I can see from the function signature that it might do IO.

This comes at a cost, namely that of reading five extra characters in a function signature, and I could kind of imagine (truly!) how that gets in the way for some people. There is a cost of writing the five characters as well (and like the author mentions, in a poorly designed codebase, this may have to go down the call stack), but code is read more often than written, so in a sense this is negligible.

Like the dynamic vs static typing debate, I feel like this ultimately boils down to context and personal taste, and some amount of intelligence as well. I'm impressed by the amount of stuff the dynamic typing / non-async crowd is able to keep in their working or long term memory while coding. I don't have that kind of mental bandwidth, sadly.

Having said all that, this argument is disingenuous in that it completely ignores the fact that the async keyword tells you something useful (rather than some made up nonsense like color), and most of the argument basically boils down to "if you ignore the benefits, this syntax has no benefits", and I really don't respect that as an argument.