@Njaard
Yes everything is God's will, but we can't just say that everything that is done is right. Think about it, if we had that attitude, Hitler would be ruling most of Europe right now. Much evil (including the murder of innocent babies ie. embryo's) has been done in the past, and it should be stopped.
@thelistman
Stem Cell Research wouldn't be able to cure your OCD because it is not the result of a loss of tissue, stem cells probably wouldn't be able to help your grandfather either, due to the fact that in order for them to be effective, you would have to grow new tissue, cut out the old damaged tissue, and then graft it into your grandfather's body. This would be a very complex and quite frankly dangerous procedure which probably has the same chance of killing your grandfather as it does curing him. Also if the cancer has spread, this procedure would be impossible, but there are different, more viable approaches to curing somebody with cancer that doesn't involve the murder of an innocent human (bacteriophages?). Even then there are other viable ways of getting stem cells, such as the umbilical cord, or baby teeth. If anybody in your family were to have a baby, they could save the stem cells from the placenta, or if you have any smaller children that are losing their baby teeth, the roots of those also contain stem cells. As blood relatives the cells should be compatible. As I mentioned before there are many ways of achieving our goals without killing people.
@Eshploded
While you value cognizance of what is happening to them as your deciding factor, I urge you to consider something else. Potential. I'm sorry to speak in such callous terms, but as humans our lives are insignificant. What matters is the potential that our lives hold. Now it comes to the matter of killing a embryo with an empty slate of potential, which literally has the ability to do anything, or sacrificing a life already in progress. Now I'm all for saving lives (I am studying to be a doctor after all), but I don't really think that cutting off another, especially one with blank potential, is worth it.