'Life starts at conception'
- Life started over three billion years ago. In direct line from parents to offsprings, there is no anorganic phase. Unless you define life as SkywardStriker05, in which case there's no problem to start with.
'How can you justify abortion?'
- By advancing the importance of therapeutic abortions:
"An abortion is medically referred to as a therapeutic abortion when it is performed to save the life of the pregnant woman; prevent harm to the woman's physical or mental health; terminate a pregnancy where indications are that the child will have a significantly increased chance of premature morbidity or mortality or be otherwise disabled; or to selectively reduce the number of fetuses to lessen health risks associated with multiple pregnancy.[11][12]" (wiki)
'It has potential to become a human being'
- Murder is "the unlawful premeditated killing of one human being by another" (Oxford Dictionaries). So legally, if it's not yet a human being, there is no murder.
'But it would have become a human'
- Probably not. "Only 30 to 50% of conceptions progress past the first trimester.[17]" (wiki)
'But it cannot speak for itself'
- Then it cannot speak against itself either.
- Do you put the non-opinion of a cell mass above the opinion of a mother or a doctor (who can evaluate the risks)?
'You're still terminating a potential life'
- Linking back to the first point, so is masturbation and celibacy since single gametes (ovules and sperms) are live cells too.