I use one argument: When does life begin. The EXACT moment.
There can be no answer, thus life begins when life begins: when the zygote is created. Thus when the life is created, it is no longer one human (the woman) but two (the woman + the baby).
I am not kidding when I say this SCIENTIFIC argument has never been defeated. The lefties just resort to ad hominem since that is all that is left.
Most of the pro-choice folks I can engage in debate have already crossed the Rubicon ... they will ultimately admit that abortion ends a human life but they will insist there are degrees of humaness or some other ludicrous excuse for their god-like powers of discernment. They know and will admit that abprtion kills a human life, terminates a human being, or terminates a real human, they just nassuyme god-like power to do so ‘for the woman’s benefit!’