Toddler tantrums are IMO an entirely different thing from general rudeness or bad behaviour.
Not long ago someone wrote a book called 'French Children Don't Throw Food'.
Er, perhaps that's because French parents don't allow them to!
I do think things have changed, certainly from my own childhood. My parents weren't particularly strict at all, and we were rarely smacked, but we had to do as we were told, since we knew there would be consequences otherwise. As for saying, 'No!' to a parent, or any adult come to that, when asked or told to do something, we'd never have dared. Ditto to any outright rudeness. I won't say we never sulked, though!
Over the years, including from my own generation, I've seen so many parents making threats which they never carry out. All the child has to do is scream, roar, abuse/hit the parent, or just generally strop long enough, for the parent to cave in.
And then they shrug helplessly, with that 'What can you do?' eye roll, and wonder why they have so little control.
Infuriating to witness - I've often had to bite my tongue.
I have to say that my Singaporean sister in law has always been far stricter with her children, than even my own parents ever were. Rudeness/disobedience is simply not tolerated. I think she's rather more extreme than most parents, but in general I gather that children in Singapore are considerably more strictly disciplined than here.