This is a serious question, and one that pro-life conservatives typically haven't bothered to consider. The answer is: even an infinite number of blastocysts can't screw in a light bulb. They can't operate a tool-and-die machine, come up with novel medical innovations, or start a small business either. The contribution blastocysts make to the American economy is precisely zero.
And yet pro-life conservatives want to say that blastocysts are people like the rest of us. What they don't seem to understand is that if we count blastocysts as persons like anyone else, our per capita GDP will drop sharply. The same goes for average productivity. And as any economist will tell you, lowering average productivity compounds over time, making life progressively poorer for all of us and greatly increasing the chances that we will be economically overpowered by countries that don't count blastocysts and embryos as persons. Countries like China.
Pro-life conservatives think they can just extend rights to everyone. They haven't stopped to consider the economic costs or the threat to our economic position in the world. It would not be too much of a stretch to say that their views put not just our way of life but the American dream itself at risk. Once we welcomed strapping immigrants who were willing to build this nation; pro-life conservatives want to replace this inspiring vision with a nation of parasites who can't swing an axe, program a computer, or dream a dream. And that's not what America is all about.
Meanwhile, PZ Myers spots an alarming new conspiracy.
Update 2: Heh.