Kids are either developed enough to understand reason, or they're not. Young children, toddlers and such, don't grasp abstract concepts like right and wrong. Rather, they seek to please the self-evident caregivers in their lives. Spanking toddlers does not communicate anything to them other than their caregiver is inflicting physical pain on them; they lack the mental capacity to establish a causal link between behavior and consequence.

Children who are old enough to establish that link are also old enough to understand that there are bad actions and good actions. As such, spanking is wholly unnecessary. If you can't communicate why something is good or bad, or why they should or shouldn't do certain things, then the solution is to find another way to explain it and use different disciplinary measures. Corporal punishment is, at best, redundant, and, at worst, abusive.

I'd also like to point out that using violence (and spanking is physical violence, no matter what euphemisms someone tries to dress it up with) is never moral against individuals for the purpose of behavior modification. The only time one can justify using physical violence is in defense of person or property, and even then, if there is another method that can de-escalate the situation without violence, then violence is completely unnecessary. I've had to physical remove my daughter from various rooms in our house a number of times, but I haven't escalated the situation by using any more physical force than was absolutely necessary to keep her from harming herself or destroying things.

If spanking is acceptable, then you shouldn't have to reiterate that you turned out fine. The only time people "turn out fine" is when they suffer some kind of adversity or problem and eventually overcome it. If you "turned out fine," you're admitting that spanking is a net negative act to suffer through.

I wish you the best of luck in raising your kids, and I hope my comment was informative in some way :)