No human being has the right to take over another human being’s body. Humans are granted free agency over their own bodies. To say there is an exception for girls and women who are pregnant is to say that such people, girls and women are not entitled to agencies over their own body. In this argument, you are giving a fetus more rights than an actual human, and are saying girls and women have less rights than people.

I haven’t seen abortion rights leading to a lack or regard of all people or human life. Quite the opposite, as you saw in the link it increases infanticide, as well as a decrease in the rights of women. Reasonable exceptions are never allowed. For example, the 10 year old girl rape victim who doesn’t even have a body big enough to carry a pregnancy would have been forced into giving a birth, which his more often than not a traumatic and terrifying experience. No child should be forced into something like that. Or Kate Cox, whose pregnancy had less than a 1% chance of surviving, and she was forced into the ER 5 times due to complications in her pregnancy and was told she would probably not die but would most likely be rendered sterile if she continued the pregnancy, yet she was a denied an abortion. There was no regard for the 10 year olds body and or Kate Cox’s desire to not harm her internal organs. In countries that ban abortion, rape of females actually increases, because pregnancy can be used as a weapon to control and destroy women. Female infanticide becomes especially high. Women are considered sub-human because they have less rights than men, they are stripped of their rights to bodily autonomy. So the slippery slope you speak of disregarding human life does slowly happen, but it happens to women when we outlaw abortion. We consider them to have less rights than other people, and thus this happens.
I do see the guise about not wanting babies to die, but that’s just a smoke screen. Conservative law makers know the fetus isn’t a human, many have daughters and wives who have had abortions and would do so again. These laws are about controlling girls and women. For example, when a man was caught poisoning his pregnant girlfriend with abortion pills, he was given less of a sentence than if she had tried to get an abortion herself.
The Bible its self literally has directions and rules around when a man can request an abortion for his wife, mostly if he believes she has been unfaithful (numbers 5:22).