This app is largely a response to the overreach of the US government. While I believe in fighting for our constitutional rights politically, private solutions are also a viable means of protest.
We probably will have liability issues down the road. Nobody said this would be easy. However, being completely transparent and publishing all our code open-source will help mitigate a lot of these issues. On top of this, by making the clients able to secure their own data, the company itself can respond to any government information requests without actually revealing any customer data.
In the Post-Snowden world, I think it is.
This being said, shouting "yes we can do this if you share copyrighted works!" means begging to be sued by the content provider on a contributory infringement basis. Hence it is far better to point to non-infringing uses, and general privacy features.