Should parents be allowed to slap/spank their kids? I don't think so. Kids who are slapped or spanked develop rebellious attitudes. No parent wants that. And some kids start to feel self conscious and have a low self-esteem. Do you want that for your kid? Instead kids should still be treated with respect when they are bad. Instead of slapping at them tell them nicely that they did something wrong. If that didn't work then send them to there room.
Parents should indeed be allowed to spank their children. Their rights as parents is to guide and discipline their children as they see fit. Although, like Uncle Ben once said, "with great power, comes great responsibility." While what you say of children developing rebellious attitudes, and low self esteem is possible, it doesnt come hand in hand. If they develop a condition so extreme that it affects their life in the future, it is more likely that they already possessed that condition, and that it wasn't caused by spanking and harsher discipline. When performed correctly, spanking can be a useful component in a parents arsenal of discipline techniques. I was spanked when I was a child and I believe my parents conducted these soankings very campy and affective. I know I wouldn't repeat whatever I did to deserve that spanking, and I certianly don't fear my parents or have any affects whatsoever. If a spanking or hitting was severe enough to harm that child in the longer run, then there is likely other contributing factors such as verbal abuse and constant attitude of frustration towards a child. when performed correctly, spanking does not have to be harmful or scarring. The parent may calmly inform their child that their behavior has warranted a spanking and may perform that spanking, while explaining to the child why they have done it. A sudden lash of frustration towards the child is not ideal, and shouldn't be the first course of action, but parents should have the right to discipline the child, and that right gives them a responsability that can be abused, or embraced correctly.