This is much older than Ben Goldacre. The earliest appearance known to wikiquote is in 1851, in Scientific American. The origin is unknown.

It also sounds like Deep Wisdom. Let's try a few variations:

Once a man's reasoned himself into something, the Devil himself won't reason him out of it.
-- this might be plausibly attributed to Thomas Edison.

No faith can long survive the light of thought,
Which as the salt sea eats away the iron:
However stoutly it may seem to stand
It yields to sleepless rust and falls apart.
When Epicurus "Atoms!" spoke, that light
Once kindled ever burned, nor all the priests
That spark could e'er extinguish from men's souls
Wherein it worked to split the true from false
And though it take a thousand years, yet still
As iron yields to rust, and stone to frost
Inexorable reason knows no sleep.
That Church most catholic that holds itself
To be the true custodian of the faith:
'Tis but fire-hardened wood, not ageless steel,
Which seems at first to gain access of strength
From that which would destroy it, but i' the end
Must split and crumble into smoking ash.
Like to the basilisk gaze is reason's light
That scours away the shadows of false night.
-- some suitable Victorian figure might be found to ascribe this doggerel to.