Is not aborting a fetus the same as taking a human life? Do you support taking human life?
That question usually results in the leftard going off on a tangent of how many people were killed in the wars by the EEEEVVILLLL BOOOOOOOSH.
If the person declares that an embryo or fetus does not become a human being until it reaches a certain gestational age, and consequently destroying an embryo or fetus which has not reached that age does not constitute killing a human being, an "abortion equals killing" argument will be meaningless to such a person, at least with regard to those embryos or fetuses which have not yet reached the age in question.
I've spoken to a number of people who are of the opinion that it is murder to kill a fetus which has reached a certain age, but believe that destruction of embryos or fetuses prior to that age is not murder. I would suggest that rather than regarding such people as being the moral equivalent of those who insist that infanticide should be legal even after birth, it would be more helpful to solicit their help in protecting the late-term unborn.
In addition to being helpful in the obvious way, such an approach could also help in another more significant way: most people in the U.S. either have had an abortion or know someone who has. Many such people are stuck in a guilt trap: they believe that if abortion is evil, then they or their friends must be evil; since they refuse to believe that they or their friends are evil, they can therefore not believe that abortion is evil. Such people will do anything and everything necessary to protect that illusion, since they believe that to be the only way to prevent them from being destroyed by guilt. In reality, the efforts to pretend abortion is okay simply make them feel worse and worse about it, when what they really need is to say "I am a human being who made a terrible mistake, but I am wiser now, and can work for what is right from here out."
I would suggest that people who had an early-term abortion (or have friends who did so) but join in the fight against late-term abortions and infanticide may find that such work helps them to make the necessary leap from having to pretend that what they did was okay, to recognizing that it wasn't but that such recognition and atonement cures guilt far more effectively than denial.
Note that the message of atonement can be delivered as a religious one or a purely secular one. Even from a purely secular psychological standpoint, recognizing that one has done something wrong is far healthier than trying to justify one's wrongs with known falsehoods.