Writers' ideas are poached all the time.
A great idea and $10 will buy you a cup of coffee: ideas aren't worth much without a good script to go with them, which is precisely why ideas can't be copyrighted.
I think about half a dozen people have seen my first feature script that I wrote years ago: yet after writing it I discovered a novel which had a similar plot and a year or so back someone released a movie based on a similar idea. Does that really mean that one of those people gave my script to the people who made the movie and sent it back to the 1950s in a time-warp so that the guy who wrote the novel could base it on mine, or that most ideas are so common that people come up with the same thing all the time?