//But sometimes spanking is a knee jerk reaction in a heated or dangerous situation where you need to put an end to it, and let the child know a few things in a short space of time.//
Kneejerk reactions let kids know things alright- it lets them know you are out of control- brilliant example of how not to behave.
I would never hit a child, it's completely wrong, unnecessary and sets an appalling example of how to respond to situations you don't like. It also causes issues for the child as an adult, my father was physically abused as a little boy by his apology of a father and Mr Cal by his stepfather. My dad had massive anger management and violence issues as well as addiction problems and ended up in prison for a long time because of that. Mr Cal went completely the other way and hates conflict of any sort and is just really, really sad about it and it's caused something of a distance between he and his Mum that she allowed it to happen.
I was never hit as a child, there is no need. My mother was never hit as a child (my grandmother is 80) so it's not a generational thing at all and I can't see why anyone thinks it's necessary?