I don't think spanking is the same as being hit with a rod, but I know many are very against spanking. I am not one of those people. I think spanking, when used very sparingly and for only extreme circumstances, can be a useful tool in child rearing. Not with a belt, not with a paddle, but with a hand and done with not a heavy hand.
There is a literal mountain of evidence that speaks to just how detrimental corporal punishment is.
At this point (actually long before this point), it’s not “many people” it’s many many long term studies on the negative impact.