Perhaps this question is woefully naive, but..... how did this become a union issue?
Yep I'd say naive. Have a look at history and you will find many instances of the crew being blamed, partly because they're no longer around to defend themselves. This is the reason many pilot bodies like ALPA have become involved.
I am not passing comment on the rights or wrongs of the crew in this accident, just highlighting reasons why the likes of ALPA become involved, to ensure the crew get a fair hearing.