My congratulations to Calidore for the win.
Now, I realize that the quote given for this round is from Lord of the Rings... Or sounds like it. But I took this in a completely different direction, which I quite enjoyed. I hope that it fits into the requirements. 
Who knows what evil lurks in the hearts of men?
Preaches of virtue, and needless sin,
Shambling home with the scent of gin,
Wearing an insipid, dopey grin,
Who knows what evil lurks in the hearts of men?
Could it be the philanthropist's song?
Ones that spends to right a wrong?
When ev'ry coin lands in the rich man's thong!
Who knows what evil lurks in the hearts of men?
A surgeon will make the cleanest jut,
To see within the darkest gut,
But, went to school for a greater cut!
Who knows what evil lurks in the hearts of men?
Could it be the poet's pen?
Who drives their passion from the fen,
To seek the cruelest of the ken?
Who knows what lurks in the hearts of men?