Some people use torrents, others use the library, and some use both. Are you asking why some prefer a library to a torrent? For them, likely ease of access and greater access to content. Effectively torrents are an expansion of the library where sharing is easier than ever.

Are you suggesting a library is only moral because of the difficulty in using it? If so, what if someone were to suggest that current libraries have become easy enough to use that they have already crossed that line?