Doesn't an Oracle go against the Blockchain principles?
The use of an Oracle does somewhat go against the founding principle of transacting without the need for a trusted third party.

As Nakamoto's whitepaper states:


  What is needed is an electronic payment system based on cryptographic proof instead of trust,
  allowing any two willing parties to transact directly with each other without the need for a trusted
  third party.


Of course the majority of transactions do not need trusted third parties such as oracles or escrow agents. But for those that do, trust is a key issue.

Other people have suggested trust minimisation strategies that can be used with oracles.


  
  multiple independent oracles
  trusted hardware
  Amazon AWS oracles