This is a very complex topic and not to be easily judged upon.
It raises most profound questions about man in a lot of ways. Not only science but moralism, religion and philosophy are questioned.
Generally I would give a yay, because I think the ability for scientific research is a gift that makes us what we are and this ability comes with the logic desire to use and explore it. Also stemm cell research can help many people in a lot of ways and maybe far more than so far is known, for we know there is still a greater part we don't know about the architecture of life. So stemm cells are inevitable if we want to go further.
On the other side the same intelligence that gave us the possibility to research, made us desire rules in order to protect human life. The most important rules we installed (at least on our industrialized islands in the world) are the human rights and every other law results from them. So here is a rather bad (maybe disgusting) example for it, but I think it works: You can't kill a person (not willing into it) in order to eat him, if you are starving in the desert. The human rights of both have to be respected.
(i know this is an extreme example, just take it as an image)
So here's "The Great Debate":
Can we sacrifice the right to live of others for our own sake?
Granted, we're talking about embrionic life, and this is where philosophy and religion or belief get into it.
Asking religiosly would be: "When does the soul enter the body?", but I ain't religious so I'll try philosophically: "When does human life begin?"
All this questions were asked in the discussion about abortion, but this topic didn't have the perspectives of stemm cell research.
Given, we decided that human life starts with birth and everything before is not to be called like that. Now the research can begin an thousands of people will be healed of their diseases and can persue their personal wealth again. Maybe in a few more years cancer could be healed and other all other deadly diseases. More and more stemm cells will be needed and man was free to raise breeding farms for embryos to supply the world with it.
This is not my opinion, but a perspective of what COULD be.
Still, I can't say what for me is just. What I can say is that we have to be helluva careful when we decide how to carry on with this. Given the possibilities of this research and its possible consequences for how human life is judged, this is the most important question man ever had to answer.