Why doesn’t what a poet is like matter to his poetry?

In a discussion today, someone commented about reviling an English professor for claiming that the quality of Milton’s poetry was unimpaired by the personal qualities of Milton himself. She couldn’t buy the notion of separating the man and the artist.

I can, and in support of my position I went and dug out this extended quotation from Edmund Crispin’s The Moving Toyshop.  The speaker is a professional poet himself.

“. . . The fact is, there’s no such thing as a poetic type.  Chaucer was a Government official, Sidney a soldier, Villon a thief, Marvell an M.P., Burns a ploughboy, Housman a don.  You can be any sort of man and still be a poet.  You can be as conceited as Wordsworth or as modest as Hardy; as religious as Cowper or as pagan as Carew.  It doesn’t matter what you believe; Shelley believed every lunatic idea under the sun.  Keats was certain of nothing but the holiness of the heart’s affections.  And I’m willing to bet that you could pass Shakespeare on the way to work every morning for twenty years without noticing him once . . . .

“Poetry isn’t the outcome of personality.  I mean by that that it exists independently of your mind, your habits, your feelings, and everything that goes to make up your personality.  The poetic emotion’s impersonal; the Greeks were quite right when they called it inspiration.  Therefore, what you’re like personally doesn’t matter a twopenny damn:  all that matters is whether you’ve a good receiving-set for the poetic waves.  Poetry’s a visitation, coming and going at its own sweet will.”