In a sense you are correct, that "connection" that was made the day of the first ultrasound was indeed between me and my unborn son, and was in a way very special and unique.
Yet, is a baby a baby because the parents believe it is? Does the baby's personhood cease if the parents cease to regard it as such? This doesn't make sense to me. Things are what they are, and people are people whether you believe they are or not.
To resort to a tired cliche, there was a time when most whites didn't consider nonwhites to be "people" per se...but they were anyway, weren't they?
I can decline to regard the law of gravity, and it will pull me just the same.
When I was very young and had known no Asians, it was easy to regard them as strange beings, almost like aliens... as if they were not quite "real". Once I had known one Asian, and realized that person as a person, I internalized the concept of "all Asians as people much like me".
I was once wishy-washy on the subject of abortion, as I said. I didn't quite have the concept of the unborn-as-people really internalized. Then I saw my son on the ultrasound and knew him as a real person... on that day, in the same manner as Asians above, I knew that class of humans called "the unborn" as all being persons, based on knowing one as a person.
Realizing on a level deeper than mere intellectualization that the unborn are humans deserving of human consideration, I could never again view abortion in a disintrested manner.
Disagree with me if you wish, I was simply explaining how I came to believe what I believe on the topic.