As a parent I think it's fundamentally wrong, hypocritical, dangerously associates discipline with pain and displays a complete lack of interest in problem solving when there's shitloads of information and methods available to reinforce good behaviour and discourage the bad. Discipline isn't just in the moment of the punishment given, something that can easily get out of control if it's all reliant on pain inflicted in a single moment, it's in the warnings and events leading up to it and after it too, and it's a damn sight harder to put things in perspective long term when you've leapt straight off the deep end to having one party in pain and terrified, something that doesn't encourage a predictable response or a long-term sense of safety. We don't let kids (or adults) attack animals and often we say 'you could hurt them easily', it's the same with kids. There's also a big reasoning difference in emotional resilience between them considering at night 'what if I lose my favourite possessions for a while' and 'what if my mum/dad loses control while hitting me'.
I don't care whether people like to split hairs between a slap and a full-on beating with weapons, relying on physical pain and fear (wait till your father gets home etc) is parenting reduced to nothing more than instant gratification and domination based on greater physical power. We largely manage to reinforce boundaries and a sliding scale of justice resolved, if not amicably, then at least safely, as adults without resorting to kicking the shit out of each other, which is seen as the complete loss of control and the event horizon where minor disagreement/punishment/restorative concession spills over into risk of serious injury and serious punishment. We are all aware of this, we can look up the logical consequences of minor infractions. Restricting access to things and activities based on prior, clear warnings is what I do. 'If you do that again, x item/trip etc is being removed'. It's done calmly, with forewarning of consequences, no negotiation, but also draws a line under the event and a visable limit of the consequences. It also reinforces that we are parents who stick to our word, are firm in our authority, are predictable/reliable, don't hold grudges and don't lose it. It's hard to be predictable when the threat is 'I'm going to attack you, and if you hit me back it'll make it worse for you'. That sounds a lot like bullying to me.
I don't think I could hit my daughter without thinking that I had completely failed not just in the moment as a loss of control, but also over a long period of time as a parent with a whole library of options and strategies available to raise a child over a period of years.
Just on the subject of toddlers, over the last few years we've been exhausted, running on little sleep and pushed towards the end of our tether by lengthy tantrums in public that resist any form of logic and reason while they burn through. At that point, I tend to view physically dealing with the tantrum in the moment, as it's a loss of control, and further discipline regarding using it as a tactic to get what she wants as almost two seperate issues. I get her to somewhere she can cool off and regain control first, and then once we've reached somewhere safe, the act of doing so often burning a lot of the energy out, then we talk about it. Of course it's extremely frustrating and has cost me an hour here and there, but ultimately has led to less tantrums and more ability for her to articulate why it happened and for me to explain why it never gets her want she wants (and also discuss consequences for any warnings given in the moments immediately prior the meltdown) in a controlled environment where she has regained the ability to understand. Consistency and remaining calm (and keeping a sense of humour regarding toddler logic when all is lost) are what led to results, it's fucking hard when you're shattered and carrying loads of stuff though. I've been almost in tears some nights after tucking her in after a particularly trying day.
I think taking away privileges works better in the modern era, but you gotta be firm about it
Essentially this. You need to be firm and clear and also, if there are two of you as parents, not undermine each other or have one of you as 'the good cop'. I found that really hard to start with, I'm a big softy compared to my wife, perhaps because she's a bit more aware of the tactics in how a girl might wrap her dad around her little finger :D I have since been educated.