The argument against the use of animals (including humans) in scientific research often concerns the assumption/fact that these species have a consciousness and it is therefore immoral to 'abuse' them in experiments, because they would be aware of the pain and such. However, it is generally believed that consciousness arises from a whole network of brain cells. A single cell, therefore, most unlikely is aware of any harm. Cells are cells, regardless of species, so why should we be allowed to use yeast for research, but not our own cells? Moreover, many questions can only be answered by studying human or at least mammalian cells (e.G. The mechanism of many types of cancer).
Embryos are not people. They could become people, yes, but so can the eggs in women's bodies. Every time the woman goes through menstruation, she kills off one of her eggs, so should we accuse her of being a murderer? Embryos can't feel pain and don't even have consciousnesses. "I think, therefore I am" We should focus more on saving the lives of our loved ones instead of contemplating the potential of life. Scientists are not killing babies, they're saving lives.