Advocates of unrestricted embryo destruction make two principal arguments; first, that 400,000 embryos left over from fertility treatments are going to be thrown away anyway, and second, that an embryo is not a human being because it is extremely tiny.
As to the first argument, the RAND Law and Health Initiative examined the matter and found that while nearly 400,000 embryos remain frozen in fertility clinics around the nation, only about 11,000 of these have been designated for medical research. The vast majority are held for future family building. Of those 11,000, only about 65 percent would survive the thawing process, resulting in 7,334 embryos. Only about 25 percent of those would likely develop to the blastocyst stage, and even fewer would be able to produce stem cells. Honest proponents of embryonic research admit that cloning of embryos would probably be necessary to obtain the optimum number of stem cell lines.
As to the second objection: Is size morally relevant? Is a 21-year-old man three times as precious as a 7-year-old boy? We can barely see an embryo with the naked eye, yet, as Dr. Hurlbut points out, from the vantage point of space, no human is visible on the Earth's surface. He quotes philosopher and mathematician Blaise Pascal, who noted more than 300 years ago that "human existence is located between infinities -- between the infinitely large and the infinitely small." Pascal continued, "By space the universe encompasses and swallows me up like a dot -- by thought I encompass the universe."
And by seeking to do the moral thing, we find our proper place in the universe.