What are embryonic stem cells and do you think embryonic stem cell research is ethical?

Any answer on here will get a lot of criticism, regardless of what someone says, so let me just say off the bat that this is MY opinion, and one that has persuaded a lot of my peers in the process of working towards my degree in molecular genetics.  Also keep in mind, I am a practicing Catholic, but still make it through the biomedical research community without having to compromise my beliefs or ethic values.

Here is a rather quick description of Embryonic Stem Cells (ES Cells):
A stem cell is a cell that has the ability to "transform" into another body cell.  Before transforming, it is called "undifferentiated," and does not have any special characteristics.  After transforming, it is called "differentiated," and has a specific function within the body (for example, parietal cells in the stomach primarily produce acid to digest your food, and muscle cells exhibit the ability to contract, giving you freedom of movement).  There are many different types of stem cells, but not all of them have the ability to turn into every type of body cell.  

The one naturally occurring stem cell that can turn into any type of cell in a fully grown human is an Embryonic Stem Cell.  These ES Cells only exist in fetuses for the first few weeks after conception, and after that they turn into all the different types of cells that make up the human body.  Scientists see these ES Cells as potentially incredibly useful, since under the right conditions they can turn into any type of body tissue you want.  Give some ES Cells the proper mix of chemical signals, and it can turn into skin tissue for burn victims, bone marrow for cancer victims, epithelial tissue for patients with internal injuries, or any other type of tissue you want.

The problem is, in order to use these ES Cells, you need to destroy the living fetus, which many people consider equal to killing a human being.  So, do you allow a developing fetus to live that can grow up into a normal human being, or do you kill that fetus in order to save the life of someone with a life-threatening injury or medical condition?  It is one of the most heated debates in bioethics, and understandably so.

So, from here on, I'm going to give you MY OPINION:

ES Cells are not the only way to get cells that can transform into all types of body cells, just the only known way that is naturally occurring.  Recently, scientists have discovered that, under the appropriate conditions, many types of cells can, under the right conditions, revert back to the same state as an ES cell.  For example, take a skin cell from somebody's arm, give it the right conditions, and watch it become as useful as an ES Cell in a few days (this is a vast oversimplification, but it illustrates the point).  This type of stem cell is called an "Induced Pluripotency Stem Cell."  

I strongly feel that scientists, such as myself, should avoid destroying fetuses, since I do consider it to be a human life.  Rather, scientists should devote research to turn these newly discovered Induced Pluripotency Cells into viable materials for therapeutic use.  So, in short, no, I do not think embryonic stem cell research is ethical, primarily because there are known alternatives that exist (still in early research stages) that may avoid all religious, political, and ethical problems.

The majority of the previous answer is accurate. I have a few corrections, however.

Embryonic stem cells do not come from fetuses. They come from embryos. (Fetuses are unborn babies past 10 weeks gestation. They're en embryo prior to that.) The embryos used in stem cell research are five days post-conception. At five days post conception, most women do not even know they're pregnant. This is why the embryos used in stem cell research come from in vitro fertilization (IVF) clinics. By the time a naturally occurring pregnancy is detected, the embryo is already too old to be used in embryonic stem cell research. Thus, there is absolutely no connection between voluntary abortion and embryonic stem cell research.

The embryos used in stem cell research are donated by the parents who no longer want the embryos either because their families are complete or because they can no longer afford to store them at the clinic. If the embryos are not donated to science, most likely they will be destroyed. Granted, some clinics offer adoption to other couples and some will implant them in the uterus under less than ideal conditions and allow them to "die naturally," but most of the time they're destroyed, or as I like to call it, "wasted."

Most stem cell researchers have never seen a whole embryo in the lab. That's because once the stem cells are extracted, they can multiply indefinitely. One embryo can literally be used to create millions of stem cells for research that can go on for years. The original human embryonic stem cells created in 1998 are still in use today.

Since 1970, 11,000 embryos have been donated to science from IVF clinics in the US. Since human embryonic stem cells were first created in 1998, most of those were donated to other forms of research than stem cells. Far more than 11,000 (as in millions) have been destroyed because they were considered "excess."

Scientists disagree over whether IPS cells are "just as good" as embryonic stem cells. IPS cells often retain the characteristics of the original cells, and are therefore not as versatile or in some cases not as predictable as embryonic stem cells.

In terms of ethics: Embryos that are destined to become successful pregnancies are not destroyed for embryonic stem cell research. Stem cell research is not creating a market for the destruction of human life (if that's what you consider a five day post conception embryo to be.) That's like saying donating the organs of a suicide victim creates a market for suicide. That's simply not true. It's trying to create a positive out of a negative situation.

Like I said, the stem cells created in 1998 are still in use in literally hundreds of labs world wide. I think there's this perception that every time a scientist wants to do an experiment they go to the freezer, take out an embryo, crack it open, and take out the parts they want. That is simply not the case. In reality, if another embryo was never destroyed, stem cell research could continue successfully for decades.

The first clinical trials using human embryonic stem cells are beginning in California. The condition they're trying to treat is spinal cord injury. If the treatment is successful, formerly paralyzed patients could walk again. Imagine the amount of money taxpayers could save in disability payments if these people can be cured. Imagine the difference in quality of life for these patients if the treatment is successful. The definition of unethical: standing in the way of their treatment.

If we really want to talk ethics, let's talk about the ethics of doctors intentionally creating 24 embryos for a couple knowing that maybe 2 or 3 will successfully implant in the uterus and be carried to term. That's what IVF doctors do every day. At least stem cell researchers haven't created human embryos. They just took a small portion of the leftovers.