As debates of this type go this one's quite civil.
Normally the problem boils down to the impossibility of two different paradigms reaching an agreement.
In the anti-choice lobby we normally see claims that even a zygote or blastocyst is equivalent to a fully grown human. This is either based on assumptions of equivalancy or on a religious belief that life is sacred from conception. Often, but not always, this opinion is coupled with one of extreme sexual conservatism, such as the advocacy of abstinance-based sex educaton.
On the pro-choice side we generally see a desire for thorough sex education and easy availability of contraception to reduce pregnancies caused by contraceptive ignorance, easy availability of the morning-after pill to cater for contraceptive accidents, and easy availability of early term abortions for those contraceptive accidents that pass unnoticed until a period is missed.
The assumptions of equivalency or sacredness mean nothing to the pro-choice lobby.
An argument showing, for example a 12 week-old fetus might look like a tiny 2 inch long human, but it ONLY looks human as it has less nerve tissue than a rat, likewise mean nothing to those who've made assumptions of equivalency or who foster a faith-based belief that restricts abortion.
Thus people argue from their respetive corners, and often the arguments mean nothing to the opposite corner.
A seemingly reasonable balance is to set an upper limit for when abortions may be performed for reasons other than the mother health, an dlet people decide themselves. However, those that feel even this is tantamount to allowing murder are never happy with such a compromise.
Yiz: what someone may or may not think or how they may have changed their opinion is not an argument that reflects whether abortion is right or wrong. For example; JCanon thinks he is Jesus. That doesn't mean he's right.