Even if we accept Judith Jarvis Thomson's distinction between "killing" and "letting die", how can abortion be anything but horrifically unethical? Suppose I have daughter that I reluctantly take care of. I would never kill her, but I miss the disposable income and free time I had before her.
Then one day I find out my daughter has rare disease and needs me to donate my kidney (or if you prefer, needs me to be tied to the machine described in violinist thought experiment). "Now's my chance!" I think. "If refuse to let her use my body, I can 'let her die' rather than 'kill' her. With my only child dead, I'll be free to live like a bachelor again. No more t-ball games for me!"
Even if you grant that I have the right to let my daughter die, it still sounds like a selfish thing to do. In fact it's monstrous thing to do. Just like we can defend Fred Phelps's right to free speech while condemning the way exercises it, we can defend a woman a woman's right to bodily autonomy while condemning the way she exercises it. Yet pro-choice people are much less eager to condemn women who have abortions than they Fred Phelps. Why should a woman who has an abortion get more respect than Fred Phelps?