I think Michael himself didn't want a son like Vincent.He would do anything for turning legitimate,following his father's wish:
"Senator Corleone...".Also states this in #3.
Kay never believed him,never realised his hard efforts to stabilize stuff.Michael's mistake, as Fredo's,was to marry an American woman.Would Apollonia ever kill his child?
He didn't want a son like Vincent--he wanted Anthony to become a lawyer and help make his enterprises "legitimate." But he needed Vincent and used him.
Kay
did believe Michael was trying to become "legitimate," but as we saw when they were dancing at Anthony's party, she was getting mighty doubtful. And, after the Tahoe shooting, that was it for her--no more belief at all.
Also one more comment:
While Michael was away for buisiness,Kay couldn't leave the house,right?I bet that even her doctor was made to go in Lake Taho to examine her.How did she arranged the abortion?Another hint perhaps for Tom?
Although abortions were illegal in America at that time (except to save the mother's life), any woman with money could find and pay a doctor to abort her. And Kay had plenty of money. Not a problem even if it were performed at the Tahoe estate.
I know Ultrasound has been around for a while but were people using it for sex determination in the fifties? Not sure.
No, ultrasound and amniocentisis didn't come into wide use until the late Seventies. I doubt that Kay knew it was a boy--how could she after only three months, absent those techniques? I think she had the abortion to declare her independence from Michael, and made up the stuff about a boy to rub it in.