Scientifically corporeal punishment isn't known to be effective. That's because of a few things.
The first one is that the punishment isn't related to the offense. By that I mean that the child doesn't learn the consequences of their actions. Let's say your kid breaks another kid's toy. A good form of discipline would be to get your kid to reflect on how the other kid must of felt, send them to apologize to the other kid and help them fix the toy. That way your kid gets a deeper understanding of what their mistake was and how to make amends for it. Whopping their ass doesn't make them learn anything, it just makes them resent the parent and avoid them in the future. Meaning the next time they make a mistake they'll be sure to never tell you.
Positive punishment (adding something unpleasant to reduce the frequency of a behaviour) - which is what corporeal punishment is - is also known to be the least effective form of conditioning. Something like negative punishment (removing something pleasant to reduce the frequency of a behaviour) is much more effective. For example putting a child in time out (removing the pleasant stimulus of interacting with others) works very well.
A lot of people mistakenly think that people who are in opposition to corporeal punishment are all bleeding hearts. Nope. It's just not effective. There's no logical argument for it.