For me this is the only relevant reason why you don't want to do multithreading or alternatively why you want to structure your multithreaded application as mos

For me this is the only relevant reason why you don't want to do multithreading or alternatively why you want to structure your multithreaded application as mostly independent “processes” that communicate by means of message queues. I don't view “Concurrency is hard to get right” as a valid argument.