The "there is no limit as long as you dont kill them" reminds me of a Rowan Atkinson (Blackadder, later Mr. Bean) sketch.
The school-principal invites the parents of a boy to school, because he has an announcement to make.
After a long story he claims that: "(...) so then i administered a severe beating, during which he (the boy) died." He also notes that this is why school would be canceled the following day so that all the children could attend the funeral.
Ofcourse the parents looked shocked, but the principal soon begins to laugh in an eerie way. It turns out that he was only joking, and although the parents find that very strange, at the same time at least they are beginning to feel better since their boy isnt dead!
The principal manages to stop laughing so as to note: "ofcourse i was only joking about that; i would never cancel school on account of that little s*it". (abrupt end of the sketch there, as you can imagine)
However hitting children is no joke. It doesnt have to do with character either, how they would
appear to be coping with it. And spanking a kid when it is very young is
not a good idea at all, since you might think that it makes an impression on it and so teaches it, but in reality it makes it afraid, and a very young kid (eg 5 years old) will see the hitting parent as a horrifying figure.
If it is the mother this will lead to severe problems later on, due to the 'split image of the mother' issue (ie one part is demonic, another is angelic).
Children do not have to respect their parents, or to love them. It is up to the parent to make himself/herself loved, and if he uses violence then he doesnt deserve any such thing. A parent shouldnt think that because the other person is his/her child they automatically have to respect/love them more than they actually deserve from other people.