In my strict Libertarian days I was adamantly pro-choice. Then one day I was waiting for my girlfriend in the downstairs area at the Chicago Museum of Science and Industry. They have a display of feti at every stage of development in glass jars.
Something about dead babies in jars speaks to your humanity. I wondered to myself how it could be legal to have human children in jars on display. I heard a woman asking the same question to her spouse. Then it dawned on me, what is the difference. We kill them at all stages of development everyday.
I defy any "abortion on demand", "non-viable tissue mass" types to challenge your beliefs and go look at that display. It will take your breath away.