deciding what others can or cannot do is a whole other moral discussion.

Cause then it is no longer connected to your body? Why would the same logic apply here? I am confused what argument you are trying to make

I disagree on that. It is a example of the emergency room variation of the trolley problem, as can be read further on here: https://simple.wikipedia.org/wiki/Trolley_problem?wprov=sfti1#Variations

Yup in practice it is probably less risky and less invasive to do it early for the host. But that is a separate question. I thought you meant to question the classic “when would it be considered murder” so that is what I responded to.

To answer your question. They consider the argument of “where do you draw the line” to be a red herring.

Consider the following: if a person is in need for a kidney transplant, or else he would die, would it be ethical to force someone to donate their kidney against their will? I think not.

Same applies to abortions. You are being forced to feed a parasitic being in your body, a being that destroys your body in the process. And not having an option to abort would be to take away your bodily autonomy.

As for the line, I think that the person making that choice is the one that draws that line. It is not for us to decide.