Your view is surprisingly common. They teach it at universities, nursing colleges, medical school, etc. It has been put about so much that it is almost like universal brain-washing. I first heard this view more than 20 years ago when I was at nursing college. So, please do not take my dissection of this view personally.
Firstly, let us take the term "autonomous". I've heard that word in several other contexts than what we are talking about here. For example: "Patient Autonomy". This means allowing the patient to have a say in their medical care.
The question arises, "Who is truly autonomous?"
The prime minister? Perhaps. The Queen? No.
A newborn baby certainly is not autonomous. A toddler is not autonomous (although they try to be

). Even an older child is not autonomous. They cannot do whatever they want to do.
Adults, living in particular countries are not autonomous either. They have to follow the rules and laws of the country.
So it is plain to see that the term "autonomous" is not a good reason to give for the termination of someone else's life.
Secondly, we have the term human being, which I have covered in my previous post.
Thirdly, "living outside someone else's body" versus "living inside someone else's body". Does the fact that the human being is living inside someone else's body justify killing it?
I think I am posting in Christian Philosophy and Ethics, so I will use the Bible to explain why I think that it is wrong. One of the commandments of Moses was: "Thou shalt not kill." There were no exceptions given.
Even if you leave religion out of it, no-one wants to live in a society where people are allowed to kill others. Their main motivation is protection of self. So, because the fetus (baby) is different to them i.e. any law affecting the fetus will not directly effect them, abortion is permitted in these "civilized" societies.
"Ah, yes, but abortion is there to protect women" is the normal response to what I have posted above. The question remains: "Do women really need abortion to
protect themselves?"
These days, contraception has advanced to such an extent that we are no longer living in the dark ages where abortion was seen as the only solution to unwanted pregnancies. Women have so many options now. There are at least two forms of emergency contraception. One of them can be used for up to 5 days after the event.
So the question remains: "Is there really any excuse for abortion, in this modern time?"