Non fiction counts. And it's good, too, provided that the person writing it is properly informed and edified upon the topic of what it is they're writing about.
Of course all writing shares that danger. All of our errors and sinful tendencies pretty much WILL poison our work, as long as we're human and suffer from ignorance and temptations. The only way to get by it is to try harder and harder towards sainthood. If you get rid of the errors and educate yourself in truth, then one's work will at least be much less poisoned. Nobody is perfect, but of course the less flawed a thing is, the better.