drunk people are just as full of shit as sober ones

I agree. The same can be said about children. Most people would put their hands in fire for a child who allegedly "never lies". I have met plenty of pro children liars :)

It is broken souls that speak the truth - the real truth.

I agree here too. The real truth-generating pain comes from a sense of awareness of the finality of our existence. Whether it comes from brain, heart or some intangible soul is irrelevant. We may romanticize it or be pragmatic about it, but most people will forget about charades and facades when they face imminent death or the end of anything they hold dear.
That sense of loss, of worthlessness brings the need or desire to speak the truth, to be honest with oneself and others.
It is true the cliché according to which we live in a cynical world, one that encourages cynicism as much as hypocrisy.