Any protection, including DRM, link obfuscation or IP filtering, makes user's life harder. If they want to post it, they will post it. But once you started the war with a customer by putting those little obstacles in their way, you can't stop it.
Imagine a different scenario, where it's easy not to pay but you only have to deal with your conscience.
Imagine _why posting a new chapter of the Poignant Guide. Randall Munroe releasing a charity comic. Stephey Fry kickstarting a funny ebook (http://unbound.co.uk/books/how-to-have-an-almost-perfect-mar...). Radiohead releasing a new album.
There are million cases when you can pirate easily but it's more fun to pay. Because you respect the artist or want to support the cause. I guess this is exactly the use case for Gumroad that I see.