It is fair comment that the open source community should not be complacent in its security auditing, but there is power in numbers.
If experts were all that was needed to assure secure computing, Microsoft would have the most secure software available. They hire the top grads, who probably have reasonably solid procedures for auditing software, and the resources to ensure the testing is done. All this results in software that is at the very least no more secure than open source software (I would argue even less secure than open source)
We may hate the thought, but the masses may indeed be smarter than the experts at Microsoft, IBM, Apple, and CA...