Although I believe that physical abuse is completely wrong, I also think people are always looking for excuses for why people turn out they way they are. If spanking isn't found to cause some mental disorders than as sure as the day is long something else will. Our current society doesn't accept things for being just because.
But in the search for those 'excuses' ( I prefer 'explanations'), some important things have been discovered. Its human nature to explore the causes and effects of things. Accepting things as 'just because' leads to stagnation. When we understand things more fully, we can change them, sometimes for the better. If someone hadn't been willing to explore the causes and effects of a variety of different occurrences and how they could be used, we all wouldn't be sitting here arguing with strangers over the internet on a computer.