Great and well expressed point about Omelas.
I like the statement "This is not a thought experiment - it is a call to action, as all of Ursula Le Guin’s pieces are", because most of Ursula' stories are about going through a journey (internal or external) and changing. And you can't express change if you don't act on it.
Reading Omelas can be that journey (through a thought experiment), but if we get stuck into debating it and never acting, there will be no change.