Open-handed spanking is not considered abuse in most places as long as the amount of force used is not excessive, however it is a fine line. Studies have shown that children who have never received physical punishment as opposed to those who have not only don't see much difference in behaviour but are statistically BETTER behaved. Thinking about it logically, introducing the idea of physical retaliation early on can only result in breeding the idea, whereas children who have never been hit, spanked or swatted tend to never act out by hitting, kicking, biting or other violence-based actions - children only know what they've learned. It is not impossible - and is it fact easier - to raise a well-behaved child without ever laying a hand on them. It seems too easy, as well, to react out of anger and call it a "spanking." Consider this: are you spanking them to teach them something, or to satisfy your own frustrations at the time?
"Discipline" is about teaching your child the right things and spanking ultimately only teaches them that hitting it okay.