So Susan Sarendon, someone who will never hear the word, "tra**y" hurled at her with contempt and hatred, thinks it's an OK term? How nice of her to tell us!

This is just another example of a cis person trying to decide for us what is offensive and what isn't. She can trot off to Hades for all I care. I find it offensive and if I hear anyone who isn't trans using the term I'll tell them so.
Words have power. Look at the effect bullying can have on people. We don't use the words fa**ot, ni**er, etc. because they are offensive slurs. "Tra**y" falls into that same category.