I had heard the quoted figure as roughly 75%, but yes the exact numbers don’t really matter.

The point is that, while logically your point follows, it is ridiculous to state that anyone who doesn’t have unprotected sex frequently is killing babies - there are thousands of variables at play, it is pointless to focus on them. Once implantation has occurred, however, there is a very good chance that a life will result, and that cannot be ignored.

A good comparison might be a house; you can make all the bricks and mortar you want, you can have all the raw ingredients, but there needs to be a specific act for a house to start taking shape, e.g. building a foundation or something - implantation being that specific act. Before that, all you have are raw ingredients that are meaningless by themselves. It is the combination of these that is important.