The reasons for banning vehicles are numerous, and I actually agree with many of them, mostly out of an environmental/conservation perspective. Reckless driving causes severe damage to plant growth, as well as animals that depend on the shore for survival - birds, sea-turtles you name it.
Alcohol-induced reckless driving also used to be quite common where vehicles were allowed on beaches, and there were several incidents were children were hit and killed or badly injured on beaches by vehicles - totally unacceptable.
I think the only vehicles allowed on beaches these days are the National Sea Rescue Institute, the Sharks Board and the SAPS. There has also been a change in the law, allowing physically disabled people to use their vehicles, but only to get access to the shore, after a permit has been acquired by the authorities
http://www.environment.gov.za/Services/ ... sabled.pdf