A popular argument in support of stem cell research is that pursuing the greater medical good for living human beings overwhelms ethical concerns about destroying non-sentient embryos.
Some maintain that the destruction of embryos is immoral, but that the use of stem cells is ethical if embryos are not destroyed.
Some people see a slippery slope in stem cell research that leads to a nightmarish world where human beings become mere commodities. The argument is that using human embryos for the benefit of others degrades the dignity of life.
As of 2009, the safety and full effects of stem-cell related technology, spin-offs and long-term effects are yet to be understood.
An exploration of stem cell research, and the ramifications of a future where new organs can be engineered, is available in Cynthia Cohen's book "Renewing the Stuff of Life: Stem Cells, Ethics, and Public Policy." University of Utah's "Stem Cell Therapies in the Future" also offers a comprehensive overview of ethical arguments surrounding the use of stem cells.