Here is an argument for abortion.
In the 20th century, medical science advanced to the point that populations began to expand at a fast rate, since the death rate was reduced across ages and societies. As a result, we have put unprecedented pressure on the resources of our planet. I expect we will eventually destroy ourselves if we continue on the path of population growth.
The natural way of controlling human population growth was through disease. With most diseases under control, we need to use a method that is artificial, which is birth control and abortion. We have seen in the West that women control fertility when given access to work outside the home as well as contraceptive methods and legal, safe abortions. The nice thing is that there is no need to force anyone to limit their fertility. Individual women can have as many kids as they want.