You know the freds where the couple are going through their first childbirth and the husband wants the Lion King moment because he watches too many American films and is clueless about the reality and therefore wants his entire family at the hospital, crowding in on what will almost certainly be a tired, traumatised wife? And how some people don't get the difference between the wife (sometimes) wanting her mother there but only rarely wanting her MiL?
Until you factor in that she's going through a traumatic medical procedure, and if that isn't the quintessential moment to define "people are either radiators or drains", well, I don't know what is.
Your procedure seems to not be that extreme, of course, Edna (we saw the film again yesterday - loved your creations!), but you are not just absolutely within your rights to demur his alleged help, you are being sensible and rational. He is no ally. You cannot trust him. Therefore, his presence would be a hindrance, not a help.
Rather more words than needed, but when I first read about the appt, I thought about the Lion King analogy.
I like the car one, though, too! 