I know a couple who had a very difficult time having children. Thankfully, modern science provided them an answer in the form of in-vitro fertilization. DOZENS of her eggs were fertilized with his sperm. Over the years, they implanted a few at a time, each time ending up with one new child blessing their lives (ok, they had twins, once).
After their 6th child, though, they suspected they were done. 8 makes for a large and blessed family.
Years later, they were certain. They'd reached an age where they no longer wished to be new parents.
They no longer wanted more children, and they were extremely uncomfortable with the ideas of either destroying the remaining embryos or donating them to other couples. Neither idea was acceptable to them.
The last option available was donation to scientific research.
Those embryos, while a part of them and alive, were not yet human life. They had that potential, but they also had the potential to be a part of research that could help save and improve the lives of countless others.
The idea of paying for embryos disgusts me. The potential for 'black market' embryos is repulsive on every level. This couple's decision, however, is commendable. The research will be done, and needs to be done - that does not mean that every we should ignore all moral implications.
After that, I want to point out that all MS Stem Cell Therapies I've heard of are autologous. That means that embryos don't enter into the discussion. The cells come from the patient. This is not really the place to discuss the moral questions of embryonic stem cell research.