People used to think it was necessary to "spank" adult members of the community, military trainees, and prisoners. In some countries they still do. In our country, it is considered sexual battery if a person over the age of 18 is "spanked", but only if over the age of 18.
For one thing, because the buttocks are so close to the sex organs, anal region, and so multiply linked to sexual nerve centers, striking them can trigger powerful and involuntary sexual stimulus in some people. There are numerous physiological ways in which it can be intentionally or unintentionally sexually abusive, but I won't list them all here. One can read the testimony, documentation, and educational resources available from the website of Parents and Teachers Against Violence In Education at
www.nospank.net.
Child bottom-slapping vs. DISCIPLINE:
Child bottom-slapping/battering (euphemistically labeled "spanking","swatting","switching","smacking", "paddling",or other cute-sounding names) for the purpose of gaining compliance is nothing more than an inherited bad habit.
Its a good idea for people to take a look at what they are doing, and learn how to DISCIPLINE instead of hit.
I think the reason why television shows like "Supernanny" and "Dr. Phil" are so popular is because that is precisely what many (not all) people are trying to do.
There are several reasons why child bottom-slapping isn't a good idea. Here are some good, quick reads recommended by professionals:
Plain Talk About Spanking
by Jordan Riak
http://nospank.net/pt2010.pdf
The Sexual Dangers of Spanking Children
by Tom Johnson
http://nospank.net/sdsc2.pdf
NO VITAL ORGANS THERE, So They Say
by Lesli Taylor MD and Adah Maurer PhD
http://nospank.net/taylor.htm
Just a handful of those helping to raise awareness of why child bottom-slapping isn't a good idea:
American Academy of Pediatrics,
American Academy of Child and Adolescent Psychiatry,
American Psychological Association,
Center For Effective Discipline,
Churches' Network For Non-Violence,
Nobel Peace Prize recipient Archbishop Desmond Tutu,
Parenting In Jesus' Footsteps,
Global Initiative To End All Corporal Punishment of Children,
United Nations Committee on the Rights of the Child.
In 26 countries, child corporal punishment is prohibited by law (with more in process). In fact, the US was the only UN member that did not ratify the Convention on the Rights of the Child.