Reading through this, I don't see any guarantee that your contract would be safe from bad oracles if the stakes are high enough and the attacker has adequate resources. If your attack is successful, you not only get steal the amount at stake in the contract, you steal what the good oracles have staked, and all with zero recourse.

Yes, there is not a guarantee, but the goal of these consensus mechanisms is to make the cost of attack greater than the reward.

In order for a successful attack, I believe you'd need to control a very large portion of all available REP. If your attack is successful, the value of your REP would likely go down (as the market is no longer trusted) so there's likely no economic incentive to do such an attack.