If I'm going to pay for a book, I just want the money to go to the author and the publisher that promoted the book, not some guy with a text scanner. At least with physical pirate books somebody put some money and effort into publishing. I don't have as strong an opinion on pirated books that nobody's making money off of.

The pirate Kindle books I've come across were poor quality (scanned without checking and editing), so I always get a refund, but it's still annoying to have to go through that.