absolutely nothing wrong with it.
Nothing is wrong with sex and spanking. Especially at the same time. a couple smacks never hurt anyone.
I joke about spanking all the time. But that's just it...a joke. I am sure lots of people love getting spanked or spanking as part of sex and that's okay, but me personally I don't think I'd like to be spanked. Actually I'm sure of it. Now I might spank YOU, but I might have to be a little mad at you first!
I don't much watch porn, but I LOVE the combination of sex and spanking. I guess it also has a lot to do with the roles of the people involved.