I think contraception has gotten quite good. I don't think the edge cases would excessively burden society in a way we'd be unable to manage. I could see a definition of contraception being something that prevents an egg, fertilized or not, from developing. And then we could define abortion as the act of terminating a developing embryo. I imagine if people had universal access to contraception we'd be more socially willing to push the responsibility of using the tools provided (and generally being sexually educated and responsible) back on the individuals involved.