-His conformation is nothing you would want to pass on.
-We know nothing of his training, but unless he's got a secret superb show record, what does he contribute to the breed?
-Is there a market for cross-breds with meh conformation and meh parents in your area?
-Do you have the facilities, money, and experience for ultrasounding, testing for genetic diseases before they pass it on to future generations, facilities for birthing, facilities for weaning, facilities to keep a stallion separate and content?
-In my opinion, a stallion should have exceptional breed-standard conformation, an exceptional track record in the way of showing, training, or usefulness (on a ranch, for example), and most of all, a stallion should improve the breed, not detract from it.