Cow/Human Chimera's - is it ethical?

http://news.bbc.co.uk/2/hi/health/6121280.stm

Ok, so now that you're probably confused, heres a summary. Embryonic stem cells are useful. They can be used to grow new cells that don't normally regenerate in the adult body. Cures for Alzheimers and other diseases might be possible through this research.

Stem cells come from embryo's. After 6 days when the fertilized egg has divided a few dozen times, its broken apart and the cells are harvested. The controversy of course is over the embryo's destruction, because technically, it could become a human being if it was implanted in a womb and left to mature.

However, scientists have done something interesting. This is basically cloning, so skip ahead if you know how this works. A fertilized cow egg is taken and the nucleus is sucked out of it. The nucleus holds all of the cells instructions, so after its removed, the cell just runs on autopilot. A nucleus from any old human cell is then injected into the egg, and voila, the machinery starts again. You would think that something identifies cow cells and human DNA, and you would be right. It's only worked a few times, and its very difficult to get it to work. However, after the human DNA starts giving out instructions to the cow egg, the egg starts dividing normally, and six days later, has stem cells we could use.

Now comes the tricky part: is this ethical? Opponents to this are claiming that making these chimera's of human and animal is morally corrupt. Proponents claim that this is a way to make human stem cells without needing expensive surgeries to harvest eggs from humans. And heres the big catch - with our current level of biological advancement, scientists arent sure if these embryo's can grow on to become humans. These cells are 99.9% human - the outside machinery is the only thing thats somewhat cow. So, what do you think? Should this be done?