Even now, I suspect that my own (moderate, along the same lines as yours) pro-choice position is informed by the fact that my peer group tends to be more pro-choice than not. It's also informed by the fact that pro-choice policies serve to advance what I perceive to be my own short term, arguably even selfish, interests. Therefore, I find being pro-choice, when its more than just a question of which public policy I prefer, to be very problematic and difficult for me.
Especially when you read something like this at the RH Reality Check blog from comedian Sara Benincasa. Notice how she comes to her pro-choice position based not on any kind of logical reasoning with regards to the unborn not deserving the right to life, etc. but is based solely on Planned Parenthood providing her with emergency contraception after a condom broke.
Planned Parenthood was, in the form of the woman who stayed at her job an hour later than necessary to talk a scared young woman through an incredibly safe medical experience. So I decided I'd throw in my lot with her and her tribe, maligned and hated though they might be.I think this is why pro-choice arguments are often so weak. The individual comes to a pro-choice position based on a personal experience or feelings (as opposed to sound reasoning) and then has an immense amount of trouble coming up with sound arguments to support the position they hold.