Is the embryo a person?
The most significant argument against embryo research is that an embryo should be treated as a human being, which would make embryo research equivalent to murder. Actually, evidence suggests that a majority of pro-life supporters, and many Roman Catholics, don't see the embryo as a person. The official position of the Catholic Church is that it is impossible to be certain when human life begins, so an embryo might be a person, so it should be treated as a person.
The benefits of embryo research
The benefits of embryo research are potentially so significant that the provide a very strong argument in favour of allowing even very controversial research. Embryology has already helped to develop technology that has helped thousands of childless couples to have babies - over 10,000 babies a year in the UK. Embryonic stem cell research promises cures to diseases that affect hundreds of millions of people, such as Parkinson's disease, cancer, spinal cord injuries etc.
Are there alternatives to the use of embryos?
There are many claims about alternatives to embryonic stem cell research, such as the use of adult stem cells. It is very hard to be certain that adult stem cells would be as effective, and therefore many supporters of using embryos say that the benefits of research, and the speed with which those benefits will become available, justify the use of embryos.
Is it acceptable to create embryos for research?
The number of spare embryos available for research is very limited. There are many suggestions about how to create new embryos - using eggs from aborted foetuses, using bovine eggs etc. Each suggestion carries different concerns. Those who see an embryo as a human person believe that it is deeply wrong to create embryos just for research.