I agree. Let's take another case. (I'd use murder as an example, but since so many argue that abortion IS murder, it clouds the issue.) So take stealing.  Stealing is against the law, but the vast majority of people do not steal, or only steal a little bit (maybe they cheat a little bit on their taxes, or take home some paper clips from work. That sort of thing. Why not? Because it isn't about the law. The vast majority of people don't steal because they think it is wrong. Most people do the right thing most of the time. 
But if people are desperate for food, or to pay the bills, or to support a habit, they are much more likely to steal. They'll feel bad about it, but if it means feeding their family, they'll do what needs to be done. Theyhave no choice.
The job is to persuade people that abortion is not the right thing to do tand make sure people are never so desperate that it seems like the only choice. 
Don't rely on the power of a law.