Changing the world we write in

My best friend and I got into a discussion a couple of days ago based off me wondering if women could be RAF fighter pilots (answer:yes). She wanted to know why I wanted to know this, and I told her it was for a story I was thinking about, in which there would be (possibly) women who flew in the RAF.

Her response was, well, if they can't be, just make it so they are. In other words, change one of the basic premises of the world you're writing in. Which in the end, I didn't need to do, but what she said lead to a debate about whether this is OK or not.

( Rambling writing discussion, with mild season 2 SGA Ford-related spoilers )