First, RapidShare offers free downloads for most (if not all) the files it hosts, but makes its money by offering paid subscriptions that significantly increase the speed and number of downloads you're permitted to request. The fact that they're making money on copyrighted material (including, but certainly not limited to, books) that they did not pay for makes the whole venture suspect, and to an extent, illegal. Legal file sharing services (an imperfect, though more easily visualized, analogue is YouTube) abound; there's no reason companies like RapidShare can't filter out copyrighted material as it comes in.
Second, I've heard others express the opinion that on-line services like RapidShare (though not necessarily RapidShare themselves) are akin to electronic libraries, and since information is available for free from physical libraries, the same should hold true for their Internet equivalents. This is nonsense (again, my opinion) for two reasons: first, libraries pay for the subscriptions and books they offer their patrons, which is not the case with free download sites like RapidShare; and second, even if a website were to pay for a single e-book and then allow limitless downloads of the text (akin to lending a book from a physical library), the number of downloads per paid copy would vastly exceed the average library's number of loans per purchased physical copy. Secondary points include the fact that physical libraries can only loan out a limited number of copies at a time (equal to the number they paid for), and they periodically need to replace their books as they wear out.
Now, I'm not against the existence of e-libraries in principle; I think with proper DRM and administrative oversight, they could work out. Then again, the threat of piracy is clearly a problem for copyrighted information on the Internet. So I ask you, meine Damen und Herren: what do you think?