Introduce the idea of a position being as ridiculous as its polar opposite
When you say you are "pro-life", you are calling those who disagree with you "pro-murder"
When you say you are "pro-choice", you are calling those who disagree with you "pro-slavery"
Because it is disingenuous to accuse people of being for murder or slavery, it's disingenuous to frame your position of this argument in those terms.
It avoids having to do the hard work of debating what's a reasonable definition for the start of life. It avoids the hard work of seeing where we find common ground
Let's do ourselves a favor and assume that we are all pro life and choice. This however does not mean I have the right to murder people
Provide multiple starting points of view on start of life. You should argue accordingly
Inception - new DNA
Heartbeat
Crossing the vaginal canal
We agree on avoiding unwanted pregnancy. How can we reduce that?