This is a really interesting topic. I used to be perfectly fine with spanking. My parents did it and I didn't know any better, and like many people, I was inclined to defend my parents actions and my own psychology, even if they had harmed me. I ride horses and work with animals so I used to use the justification that using crops etc as aids when horse riding are positive and work well with horses, so it would be similar with children. I was pretty wrong though, children are nothing like horses in that sense, and you likely wouldn't treat a foal in such a way either. Plus, while I'll use a crop as a communication aid, I would not use it for more than a quick tap.
Since studying the subject and looking into research as well as re evaluating my own experiences, evidence suggests there really isn't much benefit to spanking. I'm not talking about pop psychology studies, I'm talking about a huge body of published scientific research. The benefits are often short lived and tend to cause more damage than good. The damage is always not huge if you use spanking in what many would call the "right way", but it does seem to consistently lead to a sense of distrust between the child and the parent and is more likely to lead to their behaviour being worse in the future. Spanking also seems to have negative impact on child development, which is pretty serious and should be enough of a deterrent to make any loving parent think twice.
What is also very important to remember is that while spanking/corporal punishment is not abuse, abuse often starts with spanking/corporal punishment. It's easy to get into that mindset and then go too far with punishment, using it as punishment when it's not necessary or using it in anger and scaring the child. While loads of people would say "I would never hit/abuse my child or let my anger get out of control when spanking them", statistics show that just isn't true. For example, my own parents went over that line on multiple occasions, something which wouldn't have happened if the line had been clear not to physically harm their children even during punishment. I am sure they never thought of it as abuse, and they have told me again and again through my life that it wasn't. But it was abuse, and it was enough for me to leave home at 12 due to fear for my safety. Children are small, an adult using physical force with aggression is scary, even if you aren't leaving visible bruises, the harm is there. Imagine how you would feel if a giant started spanking you and you had absolutely no control of the situation. Then imagine the betrayal you would feel if that giant were the person you loved and trusted the most. It's a really dangerous line to walk as it is so easy to cross over. If you were in a relationship with a person who physically "punished" you every time you did something "bad", you would likely leave, and probably get a restraining order, and maybe have to get some counselling... While adults should be in control a bit more, and children do need authority, there are other better ways to punish a child to teach them not to do something again without the potential for harm to your relationship with them, or their psychology.
I do not judge parents who choose to spank their children, they usually do so out of ignorance rather than any lack of love for their children. But I would advise any parent to do their research properly or consult a professional before they choose to use corporal punishment. Child development is a sensitive time which will alter your child's psychology for the rest of their life, is that really something a parent wants to fuck with without even looking up the consequences? There are lots of things which our parents and grandparents grew up with which they would say was perfectly fine which has turned out to be incredibly unhealthy, or later seen as morally wrong after people actually questioned it, spanking is one of those things. Smack a child's hand before they do something dangerous by all means, or push your child back physically before they run into the road, that's not punishment though, that's a snap physical reaction to stop a disaster. While the child might be shocked in that situation, it's not the same as using a physical, embarrassing and often scary punishment on your child which could easily turn into abuse (even if you don't think you're spanking them that hard).
So... My answer is a firm "no, parent's should not use spanking". It is not a black and white "parents who spank are evil abusers", you cannot blame people for not knowing about invisible harm if they've never been taught, but it is pretty dam clear once you do look into it that spanking is not good news, even with the best intentions, and as it really isn't a necessary form of punishment for children and has been shown to cause behavioural issues in children, it just doesn't seem worth the bother or the risk. If anyone here does spank their children, or intends on using spanking/physical punishment on their future children, whatever your preconceptions of this which may have come from your own experiences, please take a look at some of the research on this subject and make an informed decision whether to continue or try out other techniques. I have heard "all children are different" a few times in this thread, and while that is true to a point, children really are not that different in their make up and in what can cause them harm. Much of what we do in life is learned, so the argument that some children are different and need punishment may be a vicious cycle, as in the child learns from the parent who physically punishes them, and/or develops psychological issues because of this, they may then seem to need physical punishment more in the future.