Wasn't projecting async all the way down to IO primitives.
Commented because most of the debate seems to be threads vs callbacks--with processes being unwisely overlooked.
That being said, if we're talking not about IO, but about cpu/memory bound problems... Well I'd be lying if I said it was uncommon in my career to come across people who assumed, to the detriment of simplicity, quality, and performance, that a calculation (e.g. process a list mapping op with AsParallel/parallelStream) would be aided by parallelism. That is just ignorance by Dunning-Kreuger devs who don't apply a critical eye to their own experiences.
We desperately need more isolation in software.