I just read this about abortion. It helped me to figure out some of my own thoughts on the matter. The first paragraph had me wondering, "but there's a miracle in there!" (in the fertilization; not the ejaculation). The second paragraph seemed to address my concern, but did not provide an answer. I would not be surprised if scientists are currently investigating this stuff. I'd look forward to what they find out.
I wouldn’t equate flushing sperm down the sink with killing billions of human beings any more then I would equate early abortions with premeditated murder. However there is a point when a human child in the womb is just that- a human child- not a lump of flesh. At least not any more then you or I.
When are we "taking a human life" by definition? When it has a spinal chord and begins sending impulses independent of it's host? When it's heartbeat distributes vital fluids to it's developing extremities? Or when we can clearly see REM action- the signs of dreaming- in the soon-to-be-born child?