Pros Before 2007
"The benefits of stem cell research have such a great outcome that they outweigh the ethical issues." (Cost-benefit-analysis)
"If someone is going to have an abortion, isn’t it better that we use it for something useful?"
Adult stem cells would not be that interesting because they do not have the same properties as stem cells from a fetus.
The research would give great insights about the basics of the body.
Cons Before 2007
Critics against stem cell research argued that the ethical issues of scientific work on aborted fetuses did not justify the possible benefits.
"A life is a life and that should never be compromised. A fertilized egg should be valued as a human life even if it is in its very first weeks. Destroying human life in the hopes of saving human life is not ethical."
We should (and will) develop more ethical methods (such as using adult stem cells) which will enable us to research ethically. We should wait until those methods are available.
The scientific value has been overstated or has flaws. E.g. we do not know for sure that we can use stem cells to clone transplantable organs.