If someone took something that you wrote then the copyright is yours. You should be able to have Ancestry take something like that down if you do not give the right for someone to post it.
I had my tree public for awhile, until I started to see my grandmother attached to the wrong people. Her name was Mary, how many Marys do you think there are in this world? I told the people they had the wrong person, but they never took her off. I guess wrong information is better then no information.
I don't mind sharing my information, and I do, but not for people like that. That's one reason I've never put up photos and things like that because I don't want them stolen. I think I should up up a fake tree and see how long it takes for the information to spread.