“…whether ’tis nobler in the mind to suffer the slings and arrows of outrageous [book thieves], or to take arms against a sea of [pirates] and by opposing, end them.”
Now, I ask that question with the assumption that you’ll be making your eBook available most everywhere eBooks are sold—not just Amazon (MOBI), but Smashwords and BookieJar (EPUB, PDF, etc.), and all the distribution channels they provide (B&N, Apple, Sony, Kobo, Diesel, etc.).
As long as buyers, your customers, can go somewhere to purchase whatever electronic format they want, why wouldn’t you use DRM where you can to protect against piracy?
I’m trying to figure out the downside of doing so, as I’ve seen some discussions suggesting DRM is a bad idea. Why? What am I missing?