I refer you to Toby's piece, from Larks's reply to this post. 

However, while many cases of spontaneous abortion do indeed result from chromosomal defects, this is not enough to undermine the main argument in this article. There are several reasons for this. First, it is important to note that some chromosomal defects are non-fatal, such as Down syn- drome (which involves three copies of chromosome 21). We rightly value people with Down syndrome and so, if the Claim is correct, we should also value and protect embryos with similar chromosomal abnormalities. Secondly, we may well be able to make great progress in curing chromosomal diseases through gene therapy or a similar technique. This would be difficult, but if the Claim is correct, then it would also be of overwhelming importance. For comparison, it is clearly very difficult to find a cure for cancer and we cannot be certain that a cure is even possible. However, because it is so critically important, there is still a moral imperative to continue the research. Thirdly, we may be able to use tech- niques such as sperm sorting to avoid some of the chromo- somal defects occurring in the first place. While this would not save pre-existing lives, it could prevent a vast amount of embryo death and may be technically easier than fixing an existing defect.

My bad, I meant to say, "If we can all agree to care about human beings that are already in existence, what then matters is what counts as a human being." The split between many EAs is just as you say -- some care about future lives a lot; some don't. However, I think what we all can agree upon is that humans that exist now are extremely important. Thus, what then matters is what counts as a human being.

Hey, thanks for the reply. I had read Toby's piece some time ago, but didn't cite it because I couldn't find it. Now editing the original. Overall, I think Toby's article is very pertinent, but potentially wrong. The very fact that many people do not support the "Conclusion" implies that there is a prevailing problem with the way people perceive the consequences of what they actually believe. 

"The argument then, is as follows. The embryo has the same moral status as an adult human (the Claim). Medical studies show that more than 60% of all people are killed by spontaneous abortion (a biological fact). Therefore, spontaneous abortion is one of the most serious problems facing humanity, and we must do our utmost to investigate ways of preventing this death—even if this is to the detriment of other pressing issues (the Conclusion). I do not expect many people to accept the Conclusion." [my addition: but perhaps they should?]

Regarding your other points on tractability, I personally find quite strong evidence that contraception, rather than legal barriers to abortion are the way to improve this. (see prior point about IUDs, or vasectomies)

Thanks for the link. It's good to get a sense of the scale of things. I hadn't realized that induced abortions were such a large number.

The reason I wanted to use the "human" bit was that I think the argument about "potential" is flawed. If we care about depriving the future potential of something, then we would oppose girls education on the basis that it reduces fertility (i.e. potential human beings). See https://forum.effectivealtruism.org/posts/YSz8JsCi3u7fupWHX/is-ea-just-about-population-growth.

If we care only about human beings that are already in existence, (which I think is something that most people can agree on), what then matters is what counts as a human being.

In a more political vein, I personally am staunchly in the camp of increased birth control, though my views on abortion (as shown here) are tenuous at best. There are many birth control methods, such as IUDs, that dramatically decrease the chance of an unintended pregnancy (to near 0), yet the public decides to promote greater condom use for their ability to protect against STDs. Both are needed.

Hey, thanks for answering my post. Means a lot, especially since you seem to be more familiar with philosophy than me. 

"Total utilitarians care about intrinsic value of outcomes."
- But a) death is painful b) death is the loss of future life c) parents grieve over miscarriages just as people grieve over the loss of a friend.

"Embryos must have an interest in continued existence."
- Hm, but I argue this is a temporary state. Say I give that mother nutrition and I wait 9 months. That embryo now has an interest in continued existence. In a similar vein, suicidal people have no interest in continued existence. But if I give that suicidal person therapy and wait some time, that person now has an interest in continued existence.