Is Free Will Predetermined?

In Colorado, there is a 'new' petition on the ballot which will amend the constitution to change the legal definition of 'person' to start at the moment of 'biological development' (read conception + cloning/stem cells). Now, it's pretty obvious to even the casual observer that this is another end-run attempt to legislate an overturning of Roe v. Wade. I put quotes around 'new' because this was tried two years ago and was soundly defeated. I am mentioning this here because it raises a very important and thorny issue (and no, I'm not talking about abortion, per se).

Are we our brother's keeper? Do we have a moral/ethical obligation to prevent someone else from performing an action which we see as morally repugnant and against the common weal?

Alternately, are we, as people of conscience, required to permit another to follow their conscience even if we find it odious? Are we obligated to allow the Tree of the Knowledge of Good and Evil to flourish and permit people the free will to choose a bite from the apple?

In short, where does our communal responsibility and personal responsibility begin?