Sometimes there's nothing you can do. All of those reasons are just covers for the deeper psychological motivations pushing them to circ. You can blow the reasons out of the water with facts, logic, and authoritative texts until you're blue in the face and it doesn't make a difference, because they've already made up their minds and the reasons are just the story they tell themselves as justification.
I mean, if they're Christian, Jesus Christ Himself could come down from heaven and tell them not to do it and they'd say "but it's cleaner."
The President of the AAP could come to their house and tell them it's not cleaner and they'd say "but he has to look like Daddy otherwise he'll be psychologically scarred for life."
Sigmund Freud could come back from the dead and tell them that their baby won't be psychologically scarred for life if he's left intact and they'd say "but it prevents HIV."
And on and on. The problem with trying to reason with people like this is that you're assuming that a) they're reasonable about circ and b) they've made their decision based on logic and reason, when nothing could be further from the truth. Under a very thin layer of modern civilization, people still have Stone Age brains and act on superstitions handed down from the tribe.

I'm sorry. Knowing that there's no rhyme or reason behind circumcision -- at bottom, it's a primitive social tradition that's hiding behind modern rationales -- doesn't necessarily make it any easier to accept that they're going to cut on their perfect little baby boy.