the joke was that maybe he considers spanking acceptable only because he was spanked and doesn't want to think of his parents in a negative light
There are some jokes you don't need to make. Making fun of people's parents are one of them. Last thing I'd want is some whiny bitch trying to punk my hard working parents who love me very much.
Were you trying to rile people up with this joke so you could then point out how unreasonable they're being? Is that what the end goal was?