Doctors know that human beings are in charge of their own bodies. You can't be forced to donate blood, and you can't be forced to donate organs or tissues, even after you've died. You should not be forced to "donate" the use of your womb if you don't want to either.
Doctors know that living, breathing, feeling people die ever day due to lack of organs and blood. They know that THAT is life. They know it, and will still not strap people down to take blood from them, or remove organs from dead bodies without permission from relatives or a pre-death-signed donor-card.
Tape-worms and mosquitoes, wasps and ants are also life, and more alive than an embryo is at the time when almost all abortions are made.
Does a tape-worm have more right to use your body? If you say No, why does a embryo have more right to use your body?
Abortion providers and pro-choice people are simply saying that for the first half of the pregnancy (or thereabout) the woman has MORE right to her own body than the embryo/fetus has. Once it's potentially viable outside the womb (week 21 now), the fetus has equal right to use the body.
At some time in the near future, it will probably be possible to remove an embryo from the woman's body, and grow it in a man-made "womb". Then, you can take care of as many unwanted LIVES as you want.