> For example the biggest reason anyone should want to write a concurrent program over a synchronous single-threaded one is performance[..]

I don't agree with this sentiment. Concurrency is a great abstraction, even if not run in parallel. After using CSP (in Go) for a time I don't care for other (mainstream) languages as much due to their lack of good concurrency primitives. I love writing programs as a bunch of services that work together. Feels like shell/pipe scripting or having daemons work together over sockets. Fits my brain very well.