Yes, it's an alternative, not a copy. For example, it doesn't provide "emergency library" style borrowing, and maybe this missing feature is a pro, not a con.
On the other hand, it's doing something similarly dubious with paywalled news articles in that it bypasses many news sites' paywalls and supposedly injects its own ads next to the content.
There are even many comment threads detailing their strategy to avoid legal takedown requests by serving content via an "anti-CDN" (i.e. always serving content from abroad whenever possible, to make legal actions more difficult).