Thats not the way it works....NOW. But in 1858 it was OK to baptize a child without either his or his parents consent and then steal the child from his parents because they were Jewish.
Your pint is well-taken. In fact, it's hard for me to imagine any rejoinder which would case an attractive light on this shameful case..
It seems to me that Pius IX was clearly in the wrong: the abduction of this child, Edgardo Mortara, was gravely morally offensive. Even worse is that Pius never apparently repented this kidnapping: he justified it in public and in private all his life. That's very disturbing.
And even more disturbing is that he (Pius IX) is being considered for canonization. The Church is under no obligation to canonize popes. Usually people are canonized because the Church considers their life of virtue worthy of honor and emulation; but nobody would want anybody to emulate this.
Such things were made possible by being written into the civil law of the Vatican States, and thus the Pope as head of State was certainly responsible for it. But it was never Canon Law nor a dogma of the Church per se, nor a matter of Papal infallibility.
The best I can say --- I know it sounds lame --- is that this is the only such incident I know of in the last 150 years. And after the terrible days of WWII, churchmen such as Angelo Roncalli (later Pope John XXII) and Karol Wojtyla (later John Paul II) showed heroic zeal in returning rescued Jewish children to their parents or their surviving Jewish relatives --- and this demonstrates that they did not consider the infamous legislation of the Papal States circa 1858 to be normative Catholic teaching.
You have recounted a mythical retelling of a complicated story. The same rules were in place in 1858. Your charges against Piux IX have been amply refuted. The Jewish parents hired a Catholic nanny against the law; the child was not "stolen" but in fact made his own choice. You've bought into an urban legend--one of dozens that circulate widely and are credulously believed by those who already are prejudiced against the Church. Don't take my word for it--read both sides and then make up your own mind. But you won't find both sides in the MSM--you'll have to do a bit of work. You wouldn't accept the MSM line on Hillary Clinton or John McCain, would you? Why are you so easily bamboozled when it comes to things Catholic (and many CINOs are easily bamboozled on these matters).