You're welcome. And yes, the sexual aspect needs to be discussed. But before I get to that, I remember reading a letter by a retired doctor to a magazine about corporal punishment. In my day at school boys (some girls did at private schools) were caned across the hand. Sometimes, they were caned across the backside, but not as frequently. This doctor said that he had treated a number of broken bones in the hand but never a broken bottom, and I thought, "Yes, but the reason for that is, you have a layer of fat near to where the fingers join the hand, and if the caner misses that, there are fin bones in your hand, whereas your bottom is a mixture of muscle and fat, BUT, you can still do a heck of a lot of damage with a cane, strap or belt to a backside. Roald Dahl, in Boy, described his mother's horror after he had been caned for putting a dead mouse in a jar of gobstoppers and he had a scarlet stripe where bruising was forming. He described the headmaster as, for another boy, "Raising it high above his shoulder," and he brought it down upon the boy's backside. The level of violence by the principal was unjustified.
The sexual violence comes initially from the degrading experience of a young child or teenager having to bare their backside for an assault with a hand or implement and the spanking parent having a clear view of their genitals. I believe that your father was totally out of line putting your brother, or you, over his knee like he did.
I also disagree with some "traditional" parents, particularly in the Bible Belt, saying that the father should spank the son(s) and the mother the daughter(s), but NOR do I believe that the father should spank the daughter(s) and the mother the son(s). I do believe, when it comes to punishment, the only time the father should punish (not physically) the child is if the father is around; if the mother is around and the father is not, then the mother should discipline, but not physically.