Q: "How do you begin a letter when you are angry, astonished and full of shame?" 
A: You don't. Wait until the "anger" and "astonishment" subsides and you are in control of your faculties.

That way you'll avoid stereotypes and insinuating that those who voted for Trump should in some way feel ashamed. 

By the way,  "the most vulnerable ... targeted by the most powerful" in the West are children in the womb. What other "right" counts, if not the right to life?