So you're claiming that pinterest should pay your legal bills for you? That's ridiculous. If you upload a photo that's copyrighted by someone else and get sued, why should pinterest foot the bill for that? There is no way the service would ever be viable under those conditions, because it would create an enormous moral hazard.
The thing is that pinterest makes most of its money on copyrighted material uploaded without the content of the original owner, so it encourages and makes money on copyrights infringement for the main part. Just like the Pirate Bay...
That isn't an issue because you are co-assigning your copyright to them, assuming you own the copyright. And if you don't own the copyright then it's not a valid contract, so it doesn't matter. It's not like you're legally able to sign away someone else's copyright. Which is exactly why the indemnity clause is there, to prevent pinterest from being responsible if people are dumb enough to do that.
