The petition explanation makes two gross errors:  First it states that if anyone buys, then returns a book from Amazon, the author is "out of pocket" a certain amount of money.  This is absolutely false.  You can't lose something you never had.  Yes, you have received less than you would have if the person kept the book.  But you certainly are not poorer because you are in exactly the same position you were in before that potential buyer ever appeared on the scene.

Next, it compares the sale to going into a restaurant and eating a meal then asking for a refund after you have eaten it. In the case of the restaurant, the eater has physically used up the food and the owner of the restaurant is "poorer" because he cannot sell it again, eat it himself, or do anything else with the food which was consumed.  In the case of the book, the author still has the ideas which he is free to use, to offer to others, or to modify in any way they wish, but also, as Coelho points out he is actually potentially richer because he may have gained a supporter who will advertise his work for free.

Amazon's policy is like having your books put out in millions of public libraries (which wouldn't have been possible without Amazon).  I don't know if I'm typical, but I have borrowed books in a library and because I enjoyed the work of a certain author have subsequently purchased something from them.  If I hadn't read that "free" book I might never have bought the thing I did.  If you had a choice between having your own book in just a hand full of libraries, or millions of them, which would you choose?

I would suggest that even if you received nothing, and if your book were given free to everyone on the planet, you would still be better off when it came around to the next thing you write because you would have a certain number of recipients of your first book who would love to read whatever came next.  Cohuelo gained 12 million of those, and that was just in one country.