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Steemit. Check out the Terms of Service

So Steemit, Inc. have some king of power user on this bloackchain that can remote content?
If its just new block that update the old one, then the copyright material is still available trough some 3rd party block explorer.

Steemit can influence what this site displays, and that's the only thing they are responsible for. Noone can influence what's on the blockchain, and when you're outside the reach of authorities you could provide a platform serving everything.

So steemit.com and steemd.com are filtered block explorers?
Are those block explorer code is open source?

Yes they are effectively block explorers, or web wallets or whatever term you want to use. No the steemit.com code isn't open source. Not sure about steemd.com. The blockchain code itself is open source.

Everyone should be careful what they publish.