I don't want to get into a pro or anti nursery for babies debate as I have no experience of sending a baby to nursery.
My two baby sons were each in turn looked afrer by childminders - differnent ones in each case as there is a five year gap in age between ds1 and ds2 and we moved house.
My baby sons were happy with their childminders AFAIK. I chose CMs over nurseries because they offered a more homelike environment and I believed that was important - and also they were a cheaper option and that was necessary for us, too. However, I certaintly wouldn't say I am 100% anti nursery or 100% pro childminder.
The problem that I can see, and the OP bears this out, is the degree of attachment and personal involvement a CM can have towards her charges.
This attachment can be wonderful IME
but is not always so, also IME.
I have felt at times that my childminders were telling me how to run my life and my family and their ideas about what was best for my baby were dominating too much. It was natural this could happen, I suppose, as, looking after my baby for 10 hours a day, 5 days a week they were such a signficant person in the life of baby son.
This intensity can sometimes backfire, I think. Perhaps for the OP, the father is sensing that there is this significant other in his child's life and he is wary of it. Perhaps he feels that his baby will be less under the influence by an individual carer if put in a nursery?
I am certainly not saying what is right or wrong about childminders and nurseries, just saying that the very intensity of a one to one CM relationship with a baby can be the reason why some parents fight shy of this option.