The abortion rights era wasn't the first time people denied personhood to human beings by fiat without argument. It's happened before with slaves in the United States and apparently also with women in Canada, for very different reasons.
The U.S. Supreme Court denied full personhood to slaves (not to black people as a whole, as some have claimed, and not to black people exclusively but to any slave regardless of race, and there were white slaves) only for the sake of counting how many representatives a district would have. It's not as if the denial of rights came from this. That was already assumed. It would be silly to claim that slaves have 3/5 of a person with 3/5 of the rights of a person. This was merely a compromise between the northern states that didn't want non-voting slaves to count for representation when only the much smaller voting population would wield all the power those slaves would give them and the southern states that wanted more influence without giving the people who gave them that influence any vote.
According to Bill Poser at Language Log, a Canadian woman became some sort of magistrate, and some lawyers opposed it on the grounds that she wasn't a person and couldn't carry out her duties as a magistrate. This was in 1916. It sounds unbelievable, but once you see the legal argument for it you can tell it was just a silly lawyer's argument with no basis. Once that's clear, though, it has an interesting consequence for the debate over gender-neutral language to describe groups whose gender is mixed or indeterminate.