- Why blockchain and not something else?
I'm not aware of any other system can provide the permissionless and censorship-resistant aspects of blockchain while still maintaining a coherent, single view of the network, though I admit I'm only loosely familiar with BigchainDB.
- Why published identity? I guess that idea is that all content is actually legal and there are no pirate movies / tv shows?
It's possible to publish anonymously if that is your preference. Even using an "identity" you can be anonymous, they're just cryptographically provable pseudonyms.
Open protocols do not have a legal obligation to perform censorship at the protocol level, only users of the protocol must censor (see HTTP, BitTorrent, etc.).
- How will you control who and what is uploaded? ...legal movie distributers will not use it because content will end up in P2P...
We don't. Currently over 750,000 pieces of content are available on LBRY and to our knowledge only a little over 100 are infringing.
We do receive and process DMCA takedown requests and provide a service that lists content that is illegal to access in the United States. Official applications that we release respect this endpoint, but it's not even legally clear that we have to do this (e.g. uTorrent could do the same, but does not).
Additionally, LBRY already has one Hollywood studio making films available. You can watch a James Franco film (Howl) or a David Cross film (It's a Disaster). All existing attempts to restrict re-distribution of digital content do not work and there are strong theoretical reasons to believe they never will. Hopefully more studios will eventually be as enlightened as Oscilloscope.
- There's also a problem with content like child pornography. How are you going to prevent upload of those?
This is essentially already answered above. You can read a bit more here: https://lbry.io/what#combatting-the-ugly