Horses for courses. If a quick smack with a whip gets their head into gear, I'd much rather than than bore the life out of them spending hours on 'natural horsemanship' groundwork, making them go round, and round, and round, and round in endless circles.
I'm more of the ask nicely once, then it's business, type of person. They get their chance to respond to my aid, and if they don't, then they get told. Unless the horse is genuinely fearful or confused, at which time I will still be very firm to make the answer as clear as mud for them.
As for spurs OP, like with anything, if you're a useless rider with an anger issue or no control of your lower leg, then yes you can inflict pain and injury.
A good rider can just touch the spur and get a good reaction - and I tell you what, I know I'd rather be tapped once, lightly, with a rolling spur, then have my ribs kicked over and over because my rider thinks spurs are 'cruel' ;)